Choose Music for Photos Slide Show

It has not been possible in the early versions of macOS 12 Monterey to use Music, that is not in Apple Music.

Install the update to macOS 12.3, then you can again select the music you have imported to your Music Library, as long as it is not protected by digital rights. Just make sure the song you want to use has been downloaded from iCloud, if you are using an iCloud Music Library. Songs that need downloading from iCloud or are protected will be graded out, when you try to select them from your library. For example - I added some songs I have played on my guitar and recorded with Garageband to the slideshow:

Hi

You have to add them to the Apple Music library - then you should be able to select them in the slideshow.