I have a 2019 27" imac (not pro) which I recently upgraded to Big Sur from Catalina. My projects worked fine with Catalina but after installing Big Sur I found that the timeline no longer rendered. Initially I might see "a media pending" image or just a blank screen. Trying to render from the menu resulted in "error compiling movie".
I tried restarting Premiere, rebooting, disabling and enabling clips on the timeline, changing the Renderer but nothing worked. Eventually I downloaded the Premiere Pro Beta (see https://helpx.adobe.com/premiere-pro/kb/premierepro-and-macos-big-sur.html) and it worked just fine! In fact, everything loaded a lot faster than I experienced with Catalina. So much for Adobe's claim that Premiere Pro 14.8 is fully comptabible with Big Sur! I don't have the M1 processor but the Intel Core i9,
Crash, Editing, Effects and Titles, Error or problem, Hardware or GPU, User interface or workspaces