Just updated my Mi10 UMI from v12.2.2 to v12.2.9 without any problems! Was a little bit scared because of al problems in this thread.
Thanks developers!
Update
1. Download the v12.2.9 zip to your storage.
2. Make sure you have pattern pattern unlock (at least as a backup authentication) enabled. My primaire unlock authentication is finger print.
3. Download TWRP-3.4.2B-1206-XIAOMI10-CN-wzsx150 recovery.
4. Reboot your phone in fastboot, open adb and type 'fastboot devices' and after that 'fastboot boot twrp.img'. Remember, don't flash the recovery, only boot!
5. Wait for around 2 minutes while your phone restarts in recovery.
6. Update to v12.2.9 en wipe cache/dalvik.
7. Reboot (takes about 5 minutes). DONE!
Root
1. Download newest Magisk (v21.4) from
https://magiskmanager.com/ and safe it to your storage.
2. Boot into recovery (see step 4 above).
3. Install Magisk v21.4 and reboot your phone.
4. Download newest Magisk Manager apk (v8.0.7) from link above.
5. Open Magisk Manager and check if everything is alright. DONE!
Security update: 1th december 2020
Google Play system update: 1th january 2021
SafetyNet status: PASS!