Bad screen resolution permanently crashes Poco F1

Question

In short: I used SecondScreen app and changed the screen resolution to a bad one. The app autostarts and changes my resolution automatically. This causes a boot loop. What can I do?

In detail: This is what I did on my non-rooted Poco F1:

1. installed Second Screen
2. I gave it the permissions it needed, using ADB via my PC, and other permissions it asked via UI .
3. I chose some big resolution.
4. I shut down the PC, before disconnecting the phone from PC.
5. The phone was stuck in the weird resolution, so I restarted it.
6. it is now in an infinite boot loop. :(

It starts booting normally, but than the screen resolution becomes bad (see the photo), and, before finishing the booting, it restarts again :(

At last, the recovery menu is reached and it gives me 3 options.

1. Reboot (this is the restarting loop that brings me back to the same menu)
2. Access via MI PC Suite: I cannot access the device this way; the device is not detected. It never sees the device, except in Fastboot it says: "Try connect in normal mode first then switch", but I cannot enter "normal" mode.
3. Wipe the data (if at all possible, I would prefer to avoid losing the data).

What I know:

Codename:       beryllium
Bootloader:     locked
Anti version:       1

I can get my phone into FASTBOOT and adb sideload modes, but unfortunately not in the "normal" adb mode. Can I uninstall the app somehow, stop it from autostart, undo its damage, or anything to fix the phone without losing the data?

A non boot-loop fix was done by typing:

From adb shell, type:
wm size reset
wm density reset

but I cannot find out how to do that from FASTBOOT or sideload....

Answer 1

I fixed it* by letting the phone bootloop until fully discharged. I then plugged the phone into the computer and turned the phone on as soon as it charged enough to allow me this. At that point there is a brief window where full ADB access is possible, but only because I did have USB debugging enabled after all, but the bootloop was too fast to allow full ADB access at any point.

I imagine the phone does a fuller/slower reset when discharged. At one point in the "good" bootloop it shows a nice, round, "loading" circle, and that is when I got ADB access. There is little time before "bad" bootloop is resumed.

1. This is what I kept entering in command line during the "loading" circle boot phase, until it finally indicated that I have the full ADB access by showing the alphanumeric ID of the phone and "device" after it:

   adb devices
   

List of devices attached

    03464364da54  device

2. Uninstall the culprit app called SecondScreen, by first finding its proper name, and then uninstalling it via adb:

   adb shell pm list packages | grep second 
   
   pm uninstall -k --user 0 nameOfTheAppReturnedByTheAboveCommand 
   

3. This was not enough, and the phone entered the "bad" bootloop again, so I discharged it again and reset the screen size and density (DPI I believe):

   adb shell wm size reset
   
   adb shell wm density reset
   

It works like new now.