macOS Big Sur Beta 11.1 iMovie 10.2.1 cannot do export

Big Sur

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!