Fix- iMovie flickering edit screen - Check your BT mouse
My iMovie edit screen flickers. Other fixes suggested in earlier threads are valid, but made no improvement for me (replace prefs file, open original file in QT and export highest res, restart, etc). Turns out it's my bluetooth mouse! Toggled it on/off - flicker gone. Maybe that reset the BT connection to MacBook? Hope this helps.
-B
MacBook Pro 16″, macOS 13.6