I have a brand new Mac Mini 2020, just released. I have been having weird glitches with graphics rendering, and I found this post
https://illustrator.uservoice.com/forums/601447-illustrator-bugs/suggestions/40978006-macos-big-sur-rendering-bug

Looks like it has been closed for commenting, and blame on Beta. However, I still have the issue. I am on Big Sur 11.0.1 on a brand new machine running AI 2021

I took advice and disable GPU Performance, and it seems to be working now.

Just a heads up