Develop Bugs

[Q] Can I backup any data within fastboot?

Hi Folks,
I have experienced the sadly famous boot loop issue (the one that keeps the device on the boot screen forever), not in one, but in two different devices (same model and build, 4.0.2 GSM - ICL53F).
I fixed the first one by flashing the latest stock rom (4.0.4), but of course it lost all the data, including camera pictures.
So for this one, I would like to save as much as I can. The problem is, that I can't access the device with adb since it wont boot, I just can access it with fastboot.
I have managed to enter the ClockWorkMod Recovery and perform a backup, but it saves it into the sdcard, so if I flash the phone to fix it, it will lose the backup
So, the question is: How can I either access the filesystem trough fastboot or just performing a backup that won't be lost if I have to flash it.
Thanks in advance

You said you can access ADB...but I assume you meant can't?
If you can...
http://forum.xda-developers.com/showpost.php?p=24910351&postcount=21
And pull your sd card as well.
If not...
I assume you've tried booting into bootloader and odin?

Jubakuba said:
You said you can access ADB...but I assume you meant can't?
If you can...
http://forum.xda-developers.com/showpost.php?p=24910351&postcount=21
And pull your sd card as well.
If not...
I assume you've tried booting into bootloader and odin?
Click to expand...
Click to collapse
Your assumption is right, I can't.
And yes, I tried booting trough odin and bootloader, many times, but I have read about many people experiencing this issue, most of them solved it by wiping data (and some also flashing). I know how to solve the booting issue, I just want to save as much data as I can.

mdelolmo said:
Your assumption is right, I can't.
And yes, I tried booting trough odin and bootloader, many times, but I have read about many people experiencing this issue, most of them solved it by wiping data (and some also flashing). I know how to solve the booting issue, I just want to save as much data as I can.
Click to expand...
Click to collapse
No I understand man.
The link I gave would back up your apps at least...
And your SD if you changed -noshared to -shared but I haven't had much success.
But you'd need ADB access.
Wait for another opinion if you wish.
But I'd assume you need a factory reset if you can't get ADB...
And simply flashing a rom doesn't work, right?

mdelolmo said:
Hi Folks,
I have experienced the sadly famous boot loop issue (the one that keeps the device on the boot screen forever), not in one, but in two different devices (same model and build, 4.0.2 GSM - ICL53F).
I fixed the first one by flashing the latest stock rom (4.0.4), but of course it lost all the data, including camera pictures.
So for this one, I would like to save as much as I can. The problem is, that I can't access the device with adb since it wont boot, I just can access it with fastboot.
I have managed to enter the ClockWorkMod Recovery and perform a backup, but it saves it into the sdcard, so if I flash the phone to fix it, it will lose the backup
So, the question is: How can I either access the filesystem trough fastboot or just performing a backup that won't be lost if I have to flash it.
Thanks in advance
Click to expand...
Click to collapse
You cannot backup through fastboot with a shipping bootloader, but you can access /sdcard via adb when booted in CWM, despite not being able to connect when booted normally.
1) Boot into CWM.
2) Connect to a PC.
3) Open a command prompt in the same directory where you have your adb.exe file.
4) Type: adb pull /sdcard/

Please help - locked out of my device

I disabled encryption on my nexus 5x following this thread http://forum.xda-developers.com/nexus-5x/general/guide-how-to-install-custom-recovery-t3231143
I tried flashing a custom ROM, Chroma, and it did not work. After booting the ROM, it started showing numerous apps errors (saying the apps couldn't start). I reflashed my backed up stock ROM using TWRP, but now I can't get into the phone because my PIN isn't working (I know I'm typing it correctly, it just isn't working). I tried connecting my phone to my PC to use ADB to delete the password, but it says I'm unauthorized and will not let me delete anything.
I'm currently unable to do anything with my phone. Can someone please help me get this working? This is my only phone, and without it I'm unable to make any calls.

Have you tried booting into fastboot and flashing the stock image or trying to mount storage in twrp, adding a new rom and flashing?

bdivs11 said:
Have you tried booting into fastboot and flashing the stock image or trying to mount storage in twrp, adding a new rom and flashing?
Click to expand...
Click to collapse
I was able to download this ROM - http://forum.xda-developers.com/nex...-optimized-stock-rom-aroma-installer-t3285805 - and push it to the phone using ADB, after enabling USB debugging in the Chroma ROM. The phone is still telling me there "is an internal problem with my device, contact the manufacturer". Thankfully, I had another ROM on my internal storage - if I hadn't, I'm not sure how I would have been able to get into my phone, since my PIN had been lost and I couldn't enable USB debugging.
Have you ever seen the "there is an internal problem with your device, contact the manufacturer" error?

This is a problem on the 5x and 6p, where restoring backups doesn't restore the correct pin. It's recommended you simply remove phone lock security before making a backup. Here is what I found on fixing it:
srnoth said:
After restoring the Nandroid, open ADB and:
rm /data/system/locksettings.db
rm /data/system/*.key
This should remove the pattern/pin completely, you'll have to re-secure your phone after
Click to expand...
Click to collapse
Sent from my Nexus 5X using Tapatalk

I'm about ready to throw this phone away. I can't seem to flash anything on it without it going into a boot loop and forcing me to restore. I never had any problems flashing ROMs on my Galaxy Nexus.
I just tried flashing CM 13 on it and it went into a boot loop for some reason. I'm also getting a screen on boot up that says my device can't be checked for errors, please lock the bootloader. Any way to disable that error? And I'm still getting the "your device has internal problems" after my ROM boots.

Nexus stuck in boot loop - unrooted - Backing up photos from bootloader or recovery

Hi.
Apologies if this is a very naive question, I am not particularly familiar with mods, roms and so forth.
I have rooted another phone in the past, but that is all.
The situation:
- Samsung Galaxy Nexus
- Not rooted/unlocked. Stock android automatically updated to the latest Android version supported
- Android developer option NOT set in settings
- Stuck in a boot loop: boots to android and then after a few seconds reboots, so no time to do anything
- Not sure how it happened, I had it for years, it was in my pocket and suddenly started doing that.
- Android fastboot and recovery loads up no problem
- I have tried anything I could find online to fix it: deleted cache, rebooted in safe mode, removed battery for 10 hours
- Nothing seems to fix it, it keeps rebooting
- I want to try a factory reset, but my family photos are in the phone
- Google synch seems to have stopped functioning for this device a year ago, all my 2016-17 photos and videos are locked in the phone.
Admitting there is nothing to do about the loop problem:
Is there any way I can copy photos and videos via usb while in recovery mode?
After I will reset the phone via recovery menu, hoping it will fix it. IF that does not fix it, I will flash another rom in. But I really do not want to wipe my data before backing them up.
I am assuming the answer is no, you cannot access the internal memory in fastboot/recovery unless your phone is rooted.
But I would like an expert opinion before I resolve to wipe one year of photos and videos which I will regret losing.

@mcaldo DON'T DO FACTORY RESET, EVERYTHING WILL BE LOST
which recovery are you using..?
if it's TWRP, then it's easy..
- boot into TWRP recovery
- go to "Mount" tab
- find "enable/disable MTP" button at lower options.. (enable it )
then connect your phone to that PC, where you always connected in past, ( to eliminate driver installation stage, all drivers will be preinstalled )
Regards

____Mdd said:
@mcaldo DON'T DO FACTORY RESET, EVERYTHING WILL BE LOST
which recovery are you using..?
if it's TWRP, then it's easy..
- boot into TWRP recovery
- go to "Mount" tab
- find "enable/disable MTP" button at lower options.. (enable it )
then connect your phone to that PC, where you always connected in past, ( to eliminate driver installation stage, all drivers will be preinstalled )
Regards
Click to expand...
Click to collapse
Thanks for your reply!
By recovery, I meant 'android system recovery'
It gives me the following options:
reboot system now
apply update from ADB
apply update from USB drive
wipe data/factory reset
wipe cache partition
Is any of the above useful?
Unfortunately, I do not have any alternative recovery software available
Edit: Googling I found this: "Apply update from ADB: The Android Debug Bridge allows you to plug your device into your PC and issue commands from there. "
If I can issue commands through ADB, perhaps there is a command to copy data from my phone to my computer?

mcaldo said:
Thanks for your reply!
By recovery, I meant 'android system recovery'
It gives me the following options:
reboot system now
apply update from ADB
apply update from USB drive
wipe data/factory reset
wipe cache partition
Is any of the above useful?
Unfortunately, I do not have any alternative recovery software available
Edit: Googling I found this: "Apply update from ADB: The Android Debug Bridge allows you to plug your device into your PC and issue commands from there. "
If I can issue commands through ADB, perhaps there is a command to copy data from my phone to my computer?
Click to expand...
Click to collapse
Yes, you can copy through adb commands..
Get and extract Minimal ADB and Fastboot from here: https://forum.xda-developers.com/showthread.php?t=2317790
From PC, run CMD to extracted folder directory.
Connect phone to PC, go to update from ADB(in recovery),
Type "adb device" , it will show serial number and connected..
Then "adb pull /sdcard " (if you know particular directory of data then write it like /sdcard/photos,, otherwise writing /sdcard will copy all folders from your phone. )
it will start copying to same adb folder ..

____Mdd said:
Yes, you can copy through adb commands..
Get and extract Minimal ADB and Fastboot from here: https://forum.xda-developers.com/showthread.php?t=2317790
From PC, run CMD to extracted folder directory.
Connect phone to PC, go to update from ADB(in recovery),
Type "adb device" , it will show serial number and connected..
Then "adb pull /sdcard " (if you know particular directory of data then write it like /sdcard/photos,, otherwise writing /sdcard will copy all folders from your phone. )
it will start copying to same adb folder ..
Click to expand...
Click to collapse
Thanks for the advice.
I followed the instructions closely, and nearly got there.
adb devices returns
#serialnumber sideload
so all good
but adb pull /sdcard returns
adb: error connect failed: closed
I tried several other commands with no success
kill-server and start-server work fine but do not solve the problem
adb usb returns
error closed
So, I am starting thinking that the problem is in the bootloader being locked.
However, if I unlock it, it will be wipe all my data, I understand?
Googling about it, I found this:
The behavior is status-by-design. Your stock recovery is not designed to grant shell access. Your only choice here is to somehow manage to flash a custom recovery. – Firelord Dec 30 '15 at 14:19
3
To achieve something similar to what @FireLord suggested: TWRP can be booted on many devices without being installed. For that, find a matching image, then boot to the bootloader and run fastboot boot twrp.img. Btw: you can check with fastboot devices resp. adb devices whether a device is visible to the corresponding tool. – Izzy♦ Jul 8 '16 at 19:40
So I understand one could boot TWRP without installing it, but I am not sure if that means I could do that with the bootloader locked?
I found WugFresh nexus root toolkit which seems to do that, among many other things, but again it warns that the phone must be unlocked (using the android build "Android *.* Any", I did not know what else to choose, not sure if that makes any difference as for locked/unlocked requirements)
EDIT: my fastboot screen reads "FASTBOOT STATUS - Failbootloader locked" as the last line, when trying to run TWRP without installing.

Yes, unlocking bootloader will wipe everything..
What actually you did ? Why it went into bootloop ???
I have also read that about boot into TWRP without installing.. and it worked for many one without unlocking bootloader... Don't know why not on GNex.

____Mdd said:
Yes, unlocking bootloader will wipe everything..
What actually you did ? Why it went into bootloop ???
I have also read that about boot into TWRP without installing.. and it worked for many one without unlocking bootloader... Don't know why not on GNex.
Click to expand...
Click to collapse
What actually you did ? Why it went into bootloop ???
Click to expand...
Click to collapse
A very good question, to which I have no answer, unfortunately.
The phone was used by my wife for 2 years and then by me for other 2. I recently changed the battery.
Never rooted or unlocked. No unusual apps installed. I am a very basic user, as you might have guessed, and being my only phone at the moment, I really would not risk experimenting with it.
It went very slow over the last 4 months, so I was planning to reset it.
I put in my coat pocket for a few hours, when I took it out it had a train ticked stuck to the screen and was quite warm and on the lock screen. It froze, so I took the battery out and restarted it. From then on it is stuck in a loop, not sure why really.
I have also read that about boot into TWRP without installing.. and it worked for many one without unlocking bootloader... Don't know why not on GNex
Click to expand...
Click to collapse
That's good to know. I'll research more than.
It seems there might be a problem with the fastboot drivers on my computer, even selecting them from device manager did not work. Win7 refuses to install. The ADB drivers in theory work fine though.

If you have done nothing modification to system, then wiping data should work, but i have doubt if it also wipes personal data too, on TWRP it wipes data excepting /data/media/ which contains all personal data.. but don't know about wiping on stock recovery...
I hope you will find solution as soon as possible..
Regards.
PS. I can install stock recovery and try wiping /data.. and check what things get wiped.. but i need little time for that experiment...

____Mdd said:
If you have done nothing modification to system, then wiping data should work, but i have doubt if it also wipes personal data too, on TWRP it wipes data excepting /data/media/ which contains all personal data.. but don't know about wiping on stock recovery...
I hope you will find solution as soon as possible..
Regards.
PS. I can install stock recovery and try wiping /data.. and check what things get wiped.. but i need little time for that experiment...
Click to expand...
Click to collapse
Thanks so much.
Looking at google's documentation on the nexus:
You can remove data from your Pixel phone or Nexus device by resetting it to factory settings. Resetting to factory settings is also known as formatting the device or doing a "hard reset".
If you're factory resetting your device to fix an issue, make sure that you've tried all other troubleshooting options first. Find out how to troubleshoot your issue.
Important: Performing a factory reset will erase all data from the device.
Click to expand...
Click to collapse
It would seem that indeed all data will be removed.
This point, I will research a bit more into drivers, in case that is what it's preventing adb pull from working.
I really need a working phone, so if that fails I will hard reset, then unlock, root, flash in an alternative bootloader and perhaps a rom, and put ubuntu touch in dual boot. That will hopefully prevent me from loosing data in the future.
Sorry, this is out of topic to my question, but, , could you suggest any stable, solid rom for the nexus?
I read good things of CM12, and I ran into one which seemed to do to quite well with split windows, but I do not remember the name right now.
EDIT: I remember the name of the rom now, it's https://omnirom.org/about/

A last question if you can..
I tried to solve my boot loop problem by sideloading an update from google (maguro yakju yakju-jwr66y-factory-4cadea65.zip)
It loaded it fine but then failed because the installation it says it is not signed.
Basically, being a stock bootloader recovery from Samsung, it will only sideload OTAs from samsung, not the stock ones from google..
I cannot find the samsung ones anywhere, not for the nexus anyway, just the newer devices..
By any chance do you know where I could download proper Samsung OTA zip updates for the nexus?

Well, I talked with an android developer who confirmed that, unless you have a friend working in criminal forensic technology or similar, there is no way to get around a lock on this phone to pull data out.
So, sadly, I have wiped my phone by unlocking it, flashed TWRP and then omnirom with gapps.
My photos are gone, including a bunch of stuff my kid had made and asked me to photograph for safeeping. Very safe indeed
He kept asking me why they make the lock like that, instead of allowing some kind of password, perhaps he has a point.
So, it is quite unlikely that somebody who knows as little as I did will ever read this *before* finding themselves in the same situation.
But if you do, back up your data, unlock and flash TWRP, clockworks or some alternative, and thank yourself if and when disaster strikes..

@mcaldo wiping data/factory reset in STOCK RECOvERY will wipe everything... There is very few chances to get backup...
And yeah i found something interesting..
You can flash system.img.. only system files will be corrected not anything else..
Get appropriate zip from here : https://developers.google.com/android/images
Now take system.img to ADB/Fastboot folder ( i assume you know how it works )
Just go "Fastboot flash system system.img"
It will rewrite system partition..
Another one:
See downloads on this thread..
One says NON-WIPE, if you want me to try that zip, i will again require time for that. See here : https://forum.xda-developers.com/galaxy-nexus/general/guide-restore-to-stock-unbrick-galaxy-t2065470
---------- Post added at 11:12 AM ---------- Previous post was at 11:09 AM ----------
I don't saw your reply, it was on next page.. its sad... Sorry i am late..

Updated to 8.1 without disabling Substratum overlays... device now unusable

So, I tried flashing the 8.1 Final using Chainfire like a tutorial suggested. That was my second mistake.
My first mistake was not disabling my Substratum overlays before doing the above, even though I knew better. So anyway...
I knew something wasn't right the way my device rebooted in the middle of Chainfire doing its thing, and was on the G/progress bar for a long time. I decided to dirty flash the complete factory image, and I removed the '-w' from the flash-all script so it wouldn't wipe my data.
Now the device boots, and of course I have the System UI issue because I didn't clear the overlays. But wait... it gets better!
I found this thread which has ADB commands that supposedly fix this. So I fastboot booted into TWRP to run the commands. It asks for my password- and when I enter it, it says it's invalid!! I tried numerous times, rebooted etc, and it still does not accept my passcode.
It appears I should be able to use ADB in TWRP without my passcode, so I give it a try. I am able to sideload no problem, however when I type 'adb shell' it tells me 'error:closed'. I've searched that error, which everyone says was fixed for them with either a reboot or updating their adb/fastboot. I did both of those things, and the error still persists.
I have also tried sideloading the substratumrescue.zip file I found in another thread, however it doesn't seem to be made for this systemless setup or something.
I have had to set this device up twice since I got it, and I am really not looking forward to doing it a third time, so if anyone has any suggestions that will keep my data, I would be happy to hear them out!!
What could be causing TWRP not to accept my passcode?
Why do I get the 'error:closed' when I try to adb shell?
Any help is greatly appreciated!

Ran into almost the same thing last night (not using flashfire, but with the factory flash-all.bat). Forgot to clear my theme and got the system UI error with everything borked. Even had the invalid password in twrp.
I hate to say it, but I had to just flash the factory image with a wipe and start everything over. Lost all my pics and music from the few days I had the phone. I have now learned how not to update in the future.

IrocD said:
So, I tried flashing the 8.1 Final using Chainfire like a tutorial suggested. That was my second mistake.
My first mistake was not disabling my Substratum overlays before doing the above, even though I knew better. So anyway...
I knew something wasn't right the way my device rebooted in the middle of Chainfire doing its thing, and was on the G/progress bar for a long time. I decided to dirty flash the complete factory image, and I removed the '-w' from the flash-all script so it wouldn't wipe my data.
Now the device boots, and of course I have the System UI issue because I didn't clear the overlays. But wait... it gets better!
I found this thread which has ADB commands that supposedly fix this. So I fastboot booted into TWRP to run the commands. It asks for my password- and when I enter it, it says it's invalid!! I tried numerous times, rebooted etc, and it still does not accept my passcode.
It appears I should be able to use ADB in TWRP without my passcode, so I give it a try. I am able to sideload no problem, however when I type 'adb shell' it tells me 'error:closed'. I've searched that error, which everyone says was fixed for them with either a reboot or updating their adb/fastboot. I did both of those things, and the error still persists.
I have also tried sideloading the substratumrescue.zip file I found in another thread, however it doesn't seem to be made for this systemless setup or something.
I have had to set this device up twice since I got it, and I am really not looking forward to doing it a third time, so if anyone has any suggestions that will keep my data, I would be happy to hear them out!!
What could be causing TWRP not to accept my passcode?
Why do I get the 'error:closed' when I try to adb shell?
Any help is greatly appreciated!
Click to expand...
Click to collapse
What a mess hahah! It sounds like your password file got corrupt; doing all that dirty flashing is messy. If I were you I would connect the phone to a computer and get off what data you can (most stuff is cloud now days anyway). And flash a 8.1 stock factory image using fastboot on the bootloader. You can never go wrong with flash a stock factory image. Yes you loose your data, but you get a working phone haha. If your really worried about data see if you can get MTP to work and transfer it off.

Dumbass me
Yep, that was me yesterday. Genius me sideloaded the 8.1 OTA without disabling my Substratum overlays and so I was met with the "System UI Tuner has stopped" message. Then an automatic reboot to the bootloader asking me to either "Try again" or "Factory reset phone". Guess what I had to do to get my phone working again? Had to factory reset that sh*t.
Oh well, at least I made sure to unlock my bootloader this time around before setting up my phone.
But to be fair, would've been f*cked either way even if I had waited for the OTA because it's essentially the same thing as the zip file anyways. Lesson learned: disable Substratum when you update your sh*t.

Fastboot boot TWRP beta 2, and go to advanced and sideload the substratum recovery zip and it'll fix it

Strange. I didn't disable my Themes and I had no issues at all sideloading.

fantasy2c said:
Fastboot boot TWRP beta 2, and go to advanced and sideload the substratum recovery zip and it'll fix it
Click to expand...
Click to collapse
This is exactly what I did. When it asks for your password, click cancel and it'll let you get into twrp. Go to adb sideload and sideload the rescue zip. I've attached it below. When you boot, uninstall the old overlays, then build and enable them.

I only update once a month when a new patch comes out.
I set my apps to not auto update
After a new patch comes out in the first week of the month I
-disable the overlays and remove them
-update swift black and compile new overlays
-update all my apps
-adb to recovery and flash ota
-apply new overlays
- reboot and good to go

I have done it before to you can just boot TWRP as long as you have that rescues zip on your flash drive you can do it that way too

rajlulla said:
This is exactly what I did. When it asks for your password, click cancel and it'll let you get into twrp. Go to adb sideload and sideload the rescue zip. I've attached it below. When you boot, uninstall the old overlays, then build and enable them.
Click to expand...
Click to collapse
Thought I was screwed, Thank you so much for this post.

Try formatting your internal memory using TWRP. It should be "formatting", no other type of wipe will be sufficient. Then flash your favourite ROM and enjoy!

Mi Max 3 6/128 SoftBrick - What to Do?

Hello,
I have a Mi Max 3 6GB/128GB which I got from the UK which arrived unlocked and with Global Stable ROM installed which actually updated to V10.3.3.0.PEDMIXM by OTA - I tested.
fastboot getvar anti shows failed, so I assume no Anti Rollback Protection, which I thought a little strange, it being MIUI 10 with (after OTA) June 2019 security patch.
I spent the last couple weeks setting up the phone to my liking (I have 300 apps installed) and finally finished yesterday.
Then I wanted to uninstall some Google/Facebook/Xiaomi bloatware using the excellent "Xiaomi ADB/Fastboot Tools".
I was pretty careful in my opinion to only remove the safe ones (the tool claims to only show you the safe ones) like Music, Video, MiPay, MiCloud, MiForum, MiSIM and all Facebook in the ADB section of the tool.
The I switched in fastboot and thought it would be a good idea to wipe Cache (nothing else).
Upon restart the Mi Max 3 first shows the black boot screen with unlock written at the bottom, then changes to the normal boot boot screen with MIU and the points at the bottom showing that it is busy booting. It stayed there for a while and I thought maybe it was rebuilding the cache and it took that long, but after 30 min still no luck.
Then I fired up the "Xiaomi ADB/Fastboot Tools" on my PC again and it told me the phone was in ADB mode, I could reboot into system mode, where the same thing happened - no progress in booting.
I cannot turn off my phone either, but I can switch from sastem boot (which gets stuck) into fastboot mode via ADB.
Would someone know what's wrong and what I can do to get my phone out of that bootloop while hopefully maintaining all my data and setups, on which I worked for weeks?
Thank you so much for your help!
P.S .: In case it could help: I could read out the phone properties of the Mi Max using the "Xiaomi ADB / Fastboot Tools" while it was softbricked, meaning the ro. init. persist. sys. and dalvik. values of the smartphone. I am happy to post them here, if requested.

Hi,
Do you have an SD card? If so, remove it, because as you cleared the cache, I think it might be a problem with encryption (lost reference).
In your case, I believe a reset will work again, but you will lose application configuration data. Via ADB you can backup files only.
If you do not have unlock bootloader, be very careful as you will not be able to flash TWRP or others.
Good luck!

Thanks, the phone came from the vendor with Global Stable ROM and unlocked. It may be an unofficial unlock, though I was able to install OTAs.
I don't have SDCard.
How can I do ADB backup?
I was able to flash official TWRP just a few minutes but it couldn't access data, maybe because it is encrypted. Now I think I will try and install latest Orange Fox r10 stable, which I think should be able to handle decryption, so that maybe I will be able to get at my date.
Any other advice?

Hi,
Now that you have TWRP, clear cache / dalvik from TWRP and try starting again, maybe start system.
About copy via adb follows a link below:
https://www.lifewire.com/use-minimal-adb-and-fastboot-4582201
in step 2
"
The command to move files from your computer to your phone is adb push.
To move files from your phone to your computer the command is adb pull.
"
Through TWRP you may also be able to back up. Go to (mount partitions) and select all partitions.
Make sure the TWRP MTP option is on, it will allow the device to be mounted via usb on your computer.
I use TWRP I use nijel8, it works very well.
https://forum.xda-developers.com/mi-max-3/development/recovery-twrp-3-2-3-1-nitrogen-t3866084
If you can't launch system, you will have to reinstall the Rom.
Good luck!
PS.
More help for adb.
https://forum.xda-developers.com/android/help/adb-fastboot-commands-bootloader-kernel-t3597181

Thanks for your advice!
I first used the official TWRP and I was able to flash it and start it.
But then the wipe of cache and dalvik failed.
And I could not mount data etc..
When I tried to repair the file system with TWRP I got error 255 - unable to repair data from fsck.f2fs.
Then I saw in your signature that you use nijel8's TWRP and I read that thread, and I started to understand, that my TWRP errors most likely originate from TWRP not being able to decrypt my partitions.
However, towards the end of the thread it seemed that nijel8 stopped working on that project and then Xiaomi once again changed the encryption in MIUI 10/Pie and so it was recommended first to use an obscure Chinese TWRP and then to move on to Orange Fox Recovery Project, which supposedly can handle the decryption better. So that's what I got and I am just about to install it and see if I can rescue or even repair anything.
If you have any other tips for me, I would be very grateful.

You have explored the possibilities well, at the moment I dont have more options regarding current system recovery / backup.
The encryption error resolves you by formatting the user partition by TWRP, in the option to format f2fs plus the installation of a custom Rom or Xiaomi.eu.
Look for tutorials and other reviews before testing these procedures.
Remember that there is a big achance of your ARB model as well.
Good luck.
PS. You can try dirty flash. Find an recovery Rom same version, and flash via TWRP.