In the Show Package Contents you can open a project's folder and see and play the original media, but you cannot play the project itself from Show Package Contents. Don't move or modify anything in the Show Package Contents folder. You can copy things but you don't want to be changing anything so as to avoid possibly corrupting the iMovie library.
The good news is that the projects are intact in your iMovie library.
Try deleting/resetting preferences and see if that restores the link to the iMovie app. 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.) Now see if your project icons are showing in the projects browser screen. 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.
You could also try booting up in Safe Mode and, after everything loads, immediately shut down and reboot in normal mode. Then see if iMovie works properly.
Start up your Mac in safe mode - Apple Support
You could also try looking in the iMovie Backups folder to access an earlier automatic backup of your iMovie library. 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 library. Navigate to your projects browser (where your projects are displayed as icons) and see if your projects are intact. Opening a previous library backup will not overwrite your current library.
-- Rich
