12.0.1 was also laggy... This as the same issues, and in 1st boot I couldn't make calls... Fixed after manual cleanup and reboot.
Worst device/support I've seen from xiaomi.
Yes happens with miui 11 and 12... a device to forget.
Worst device I've ever had ... and with Low WiFi speed (2.4ghz) with bluetooth on...
Prefer my good old mido device :/