New mi 11 problems crash just starts over


Aug 24, 2021
hello i'm from germany unfortunately my english is not that good.
I got my Mi11 in April. It went really well for a month, an update came after a month, since then I can no longer use it. there are always problems it makes a restart when i start an app, even if it is in my pocket i pick up the cell phone and i see that i should enter my pin. I got the mi11 back from service two weeks ago. They wrote that it was due to a third app and reset the mi11 for me. I've already tried to deinstalate every app to see which one it is unfortunately without success.
I'm just dissatisfied and don't know how I can continue to throw 900 euros in the trash