for me TWRP is able to flash the rom now since 3.5.2_11 TWRP been running 21.10.20 and the global a12 (the one that apparently caused some phones to brick) through TWRP and no issues what so ever
None of the problems described on Xiaomi.eu are suffered by the stock beta. Flash beta with fastboot method alwaysAll TWRP sucks actually on A12... They can't decrypt data. It's not for nothing Xiaomi.eu and others dev purpose the fastboot version.
It's simple, and safe, just be sure the file downloaded is genuine by checking CRC/SHA1 before flash
But i advise to people have problems and serach a stable roms bugs free to stay on a stable A11 for the moment.
You have to unblock it, you will have to apply for it and wait a week to do it.
i took the risk and went for it. first impression my heart was pounding hoping it wouldnt brick my device. i was on latesr xiaomi eu stable build, install the twrp recommended here, formatted my data, flashed the zip, it output some errors but it flashed i formatted again, twrp said there was no os installed but i just rebooted and it booted fine. and yes MIvideo is not working. here some screenshots. Also there are some changes visually and animation wise and at least as a first impression i does seem more fluid and responsive.