[Android General] alec.claire:
I did what you said with boot and system in the previous post and no luck.

When I push down Power+Volume-Down after the successful flash nothing happens with this combination expect that the phone powers on and goes into a boot loop. Be some miracle the phone booted up to system but later after restart again boot loop.

How to open F1 Play? Yes, there are two screw on the sides of the USB-C port. Unscrew them and pop the back cover with guitar pick. I don't know what exact screw size it is since i bought whole bunch of "mobile devices screwdrivers" on Aliexpress and just used the one that fitted. Also be gentle when taking of the back cover as not to rip off the fingerprint sensor's ribbon-cable which you need to push out of the cover as it is glued to it.

EDIT:

Some progress has been made, but not much.

1. When I plugged the turned off phone to the charger it turn on and right into the system. I noticed that MEID number was missing and I restored it according to these instructions (need few tries and switching USB port in my PC - some only charged, some connected to the device) - https://community.umidigi.com/forum.php?mod=viewthread&tid=18634&extra=page=1.

2. After that the phone booted into system. I've enabled developer options and once again marked the option responsibility for supposedly unlocking bootloader.

3. Installed Minimal ADB from XDA - https://xdaforums.com/showthread.php?t=2317790. Then I connected the phone with fastboot mode turned on from recovery, ran Minmal ADB and typed only a few commands from here (the ones mentioned returned errors or simply didn't work) https://www.theandroidsoul.com/unlock-bootloader-via-fastboot-android/:

adb devices

adb reboot bootloader

fastboot devices

fastboot flashing unlock

Later the text appeared on the screen whether or not to unlock the bootloader Vol+Up for yes and Vol-Down for no - that didn't work before (with enabled bootloader unlock in Developer options and missing MEID). I pressed for yes and ADB returned affrication that indeed the bootloader has been unlocked.

4. After that, I was finally able to flash TWRP. Worked super slow. You have to restart of turn of and start again the phone for the recovery (TWRP as well as the stock one) to work on normal speed. There is a method to getting into this phones recovery. While UmiDigi logo is displayed press and hold Vol+Up and fidget power button. Then it should enter recovery. It's ungodly difficult to enter something so necessary - someone who thought of it this way should be shot.

5. I flashed the Magisk form the SD card as storage in encrypted as well as other partitions expect the system one - which is weird. Does anybody have any info how to decrypt other portions? I've keept seeing on forum something about nvram but no info how to decrypt it or why.

6. I flashed the extracted AOSP .img file from .xz file using Windows app <i>7z</i>. I used <i>system-quack-arm64-aonly-gapps.img.xz</i>. The image was downloaded form here: https://github.com/phhusson/treble_experimentations/releases/tag/v204

7. After that I flashed Magisk again.

8. In the mean time I was getting <i>E:recv error on uevent</i> on every step of the way with anything I've been doing in TWRP.

9. F-in bootloop again.

I'm thinking this is some encryption of some partition related issue.