Thanks for replying.
Yeah, I already did one factory reset but it started to appear again.
I wasn't sure if these problems are common and already known.
Based on the number and severity of problems I thought that I got faulty device with a hardware defect, which cannot be fixed with new software..
I purchased my Mi 9T in april in Germany and got several problems (see list below).
The problems first appeared with MIUI 11.X and I already did one factory reset without succes..
184.108.40.206 Stable (QFJEUXM)