using itunes music on imovie

Is your system pre-Catalina? The audio display in the iMovie media side bar is a little different with pre-Catalina. For pre-Catalina, there will be an iTunes library item in the iMovie media sidebar on which you can click to reveal all of the non-DRM projected songs that are downloaded (not in the cloud) into the the iTunes library.

For post-Catalina, download your purchased songs into iTunes and from there drag them to your desktop and into the timeline of an iMovie project. Apple Music, however, cannot be used in iMovie because all of the songs are DRM protected.

--Rich