Hi,
The first thing to do is to try deleting/resetting preferences. To delete/reset preferences, open iMovie while holding down the Option and Command keys and select to delete preferences in the box that appears. iMovie will open in a new empty library. Reopen your old library to get back to your projects. (To reopen your old library close iMovie and go to your Movie folder or wherever you have your old iMovie library stored. Double click on the library’s icon. iMovie will open in that library.) Possibly you may need to reboot to set the changes. Deleting
preferences is a safe procedure that will not cause data loss or disruption to your project.
If deleting preferences doesn't work, try going to the iMovie backups folder and opening a previous automatically saved backup of your library, that occurred immediately before the crash occured.
To get to the iMovie Backups folder, follow this file path from the Finder menu:
Go/Home/Library/Containers/com.apple.iMovieApp/Data/Library/Caches/iMovieBackups
NOTE: If running Ventura or later, in the above file path substitute iMovie for com.apple.iMovieApp. So, for Ventura, the file path would read:
Go/Home/Library/Containers/iMovie/Data/Library/Caches/iMovieBackups
When you get there you will see a list of previous backups of your iMovie library. Click on one dated just before your issue started. iMovie will open in that backup library and will not overwrite your original library. In the backup library navigate to your projects browser (where your projects are displayed as icons) and see if your projects are intact and play properly.
-- Rich