Photo Library 'Photos' not showing in iMovie Libraries

Go to System Preferences>Security & Privacy>Privacy and click on the Automation icon in the Privacy sidebar. In the display box at the right, scroll to iMovie and Photos should be listed under it. Confirm that the box next to Photos is checked.

-- Rich

You might be right. When you upgraded to Catalina your Photos app automatically upgraded to Photos 5 from Mojave's Photos 4. Then when you switched back to Mojave you reinstated Photos 4 and perhaps the link was somehow broken with iMovie. But then, reinstalling iMovie should have re-established the link.

Try resetting the System Management Controller:

https://support.apple.com/en-us/HT201295

Also try booting up in Safe Mode (see Finder menu for instructions) and, after everything loads, shut down and reboot in normal mode.

Maybe it's just a matter of sequencing. Try closing iMovie and Photos. Then open Photos and park it on your dock. Then open iMovie. See if it connects.

As a side note, even though the Photos item is not showing in the iMovie sidebar, you can still directly drag your photos and videos from the Photos app into iMovie.

If still nothing works, I would suggest contacting Apple Support. Click on the Contact Support item in the upper right hand corner of this forum's screen. Navigate to a place where you can enter your phone number or make a telephone appointment. The techs there are pretty savvy. Plus, they have the capability of remotely accessing your computer, that we can't do here. If you follow that route, and have time to post back, let us know what results you got.

-- Rich

By any chance are your photos stored in the cloud? iMovie won't read those. If you are using iCloud Photos with optimize storage turned on the photos won't be read by iMovie. You would need to download them to your physical Photos library.

-- Rich

Likely iMovie is not authorized to access Photos. Go to System Preferences/Security and Privacy/Privacy/Automation and check the Photos box under iMovie.

-- Rich

Have you tried re-downloading iMovie? If not, try that.

To update/redownload iMovie 10, drag your iMovie 10 app from the Applications folder into the trash, but do not empty the

trash. Sign in to the app store and open your purchases folder by clicking on your name at the bottom of the app store side bar. You will see your purchases displayed, including iMovie 10. Redownload/update iMovie from there. If not successful, drag your present iMovie app out of the trash and return it to the Applications folder.

-- Rich

Yes, dragging is a good workaround.

Still, it's puzzling why iMovie won't link with the Photos library. Are you possibly in a different user account than the one in which the Photos library was originally designated as the system library? There can be only one system library per account, and two accounts cannot share the same system library. At least, I believe that is the case. Try a test by creating a new Photos library in your account, and designating it as the system library. Populate it with some photos. See if iMovie will read it.

-- Rich

I think at this point you might benefit from contacting Apple Support and talking to one of the savvy techs there. Click on the Contact Support item in the upper right hand corner of this forum's screen and navigate to a place where you can provide your phone number. Apple Support has the capability of remotely accessing your computer, that we cannot do here. See if they can come up with an answer.

-- Rich

Try opening iMovie while holding down the Option and Command keys and selecting to delete preferences in the box that

appears. iMovie will open in a new library. Reopen your old library to get back to your projects.

-- Rich

One more thing: In the privacy preferences box, try unchecking iMovie, then restarting your computer, and then opening the privacy preferences and re-checking iMovie.

-- Rich