I am doing a lot of testing on an M1 Mac. Premiere Pro and Media Encoder Beta are now Universal apps and they are both working amazingly well. The After Effects beta and AE 2021 are both still intel (rosetta) but I am having very few problems with either version. I have not installed 2020 on the test machine but I do know that it is pretty easy to foul up the display of a track matte or matte effect if you have draft 3D enabled. Check the Comp Panel settings. Unfortunately, you cannot easily see the Draft 3D setting unless you have or temporarily add a 3D layer. Draft 3D kills the alpha. Fortunately, if you click Final Quality in the Comp Panel, Draft 3D is reset.
Even running in Rosetta, I'm finding AE amazingly capable and fast on my bare minimum MacMini.