Same problem with 2017 iMac. Just upgraded to Big Sur. Now launching apps takes minutes as the icons bounce up and down. No indication in Activity Monitor of anything taxing the system. Tried to return to Catalina with no success. Used Internet Recovery Mode to attempt a clean install from scratch and I'm still having the same problem. Lots of spinning rainbow wheel and waiting, waiting, waiting.
jrpembe
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution