I also start suffer at thus issue very first time when i was updated on big sur when it was released. macbook pro 2020 16” i9 and radeon graphics. i have two screens whit dell new displays connected to lenovo tb3 dock setup was working just fine before big sur bit not after that. my primary screen is flickering on top of screen and not stop until I shutdown the display power and wait 5sec and then power it on again and after that it works just fine until i shutdown the mac… so something related to graphics drivers on big sur… hope Apple fix this on updates or next macos release.