For software developement reason, I tried to catch up the latest beta OS in order to discover issues or problems before its offical release. So I joined the Apple beta software program and upgrade my mac to Big Sur Beta 11.1 just last week.
It was all good until I found this problem.
iMovie app cannot export file anymore!
Because the export button is gone on Big Sur Beta 11.1!
It’s a joke, right? A movie produce app cannot produce movie?
For comparison, you can see the export button on Catalina.
So either do not upgrade macOS to BigSur Beta 11.1 ,or do not upgrade iMovie to 10.2.1. Otherwise your iMovie work gonna be suspended!
Updated: 12/16/2020 macOS Big Sur official release 11.1 and iMovie 10.2.2 have fixed this bug.