I am using 10.0.0 on an Raspberry Pi 4.
It was working correctly. However while watching a 4k movie the system crashed. When it rebooted it was still in 3840x2160p with HDR enabled--although after playing a random file it returned to the normal--but now when I try to play that, or any other, 4k movie it doesn't scale to full screen. The resolution changes on the TV and HDR is enabled but the movie only plays in the top left 1/4th of the screen. I've tried going through Video Calibration and while everything scales correctly during it, as soon as I exit back to the movie, nothing has changed.
I am assuming some configuration is corrupted but the documentation doesn't make it clear what should be deleted to return to default configurations.