photos and photo albums do not show in iMovie

Have you enabled your Photos Library as the System Photo Library?

• Open Photos, if it is not running.
• Go to the menu "Photos > Preferences > General".
• Click "Use as System Photo Library". This option should be grayed out.
• Then restart Photos and iMovie.

If you are using iCloud Photos, you will only be seeing the photos and videos, that have been downloaded from iCloud. Before you try to use items in iMovie, browse them in Photos, to force a download from iCloud.

Can other applications see the photos from your Photos Library? For example the Preview.app?

As a test: Launch Preview, the go to the File Menu, click File > Open, then scroll down all the way, until you are seeing "Media" in the sidebar of the Open dialog and click Media > Photos and wait for your Photos Library to appear.

Does your Photos Library appear after some time?

If even Preview cannot show the Photos Library, there may be a problem with the library. What have you already tried with Apple Support?

What is the file format of the image files? Does iMovie have access to Photos? You may want to check the System Preferences > Security & Privacy > Privacy for "Photos".

Does

To cover the bases, make sure that you are updated to iMovie 10.1.14, as that version fixed an issue that prevented media from appearing in the Photos library browser when using iMovie on macOS Catalina.

Along the lines of what I think that léonie is saying, if you are using Optimized Storage with iCloud Photos, that also could cause Photos app media from not appearing in iMovie.

-- Rich

Where is your Photos Library stored? Is it in your Pictures folder?

Are you using iCloud Photos?