Hey, I just updated directly from MIUI 10.3.15 (Android 9) to MIUI 11.1 (9.11.21 beta) (Android 10) with no problems:
unlock bootloader (Follow the tutorial, including TWRP installing)
install twrp ( rus that's in this thread) via fastboot (WITH .BAT FILE) and REBOOT TO TWRP (critical step) by...