This is one of the most annoying problems users have reported after updating to Android 11 and it can make your hair stand on end. The good news is that not a problem with the mobile screen, but rather the software.
As you may have noticed, it happens when you use an app in full screen or view videos, for example, Instagram videos and stories. How is it solved? This problem should have been fixed with one of the latest updates, but if you continue to have this lag or flicker, you can try some options so that it does not become a headache.
For example, some users have temporarily fixed it by disabling adaptive brightness . An option that you will find in Settings >> Screen. And on the other hand, in the Colors or Screen Mode section, choose the "Natural" option.