Lauda89 Great advice above - just know that you're not alone, almost everyone in this forum has a similar problem and it's normally not simple to diagnose. At least in your case you should be able to roll back to a fully working setup by going to your pre-November 2020 setup.
And once you have a working setup again, I'd recommend using something like Acronis True Image or similar to take a snapshot clone of your PC that you can return to easily if you start experiencing problems again.
Keep us in the loop if the switch back to 1909 works for you - as you're within 30 days you should still be able to roll back to that version by typing 'Reset This PC' in the start menu and using the option to roll back. Good luck!