How do I recover lost content after updating iMovie on Mac?

iMovie stores content in its iMovie Library.imovielibrary file.

Updating the app should not have caused it to lose the file however.

When iMovie cannot load the imovie library file for any reason it creates a new blank one.

Was your iMovie library stored on an external drive?

Or outside the usuall path in your User folder / movies?

Or somewhere the iMovie app cannot find it?

You can try quitting iMovie completely and then holding the option key when you open it again, and it should show a list of iMovie files it can find, you can choose one of them or click on Locate and navigate to wherever you may be storing your iMovie library.