Generally, the metadata that Roon uses is often not complete in the sense that it doesn’t necessarily recognize a track that has a composer tag as an actual composition. There seems to be no way to force Roon to identify a track as a composition if this info is not coming from the metadata provider. Adding a composer file tag to such a track does not help, I tried. This is more frequent if the artist or album is less well known.
Check the track info by clicking a track’s three-dot menu. Tracks that are recognized as a proper composition have a menu entry to go to the composition. Other tracks don’t, and adding a composer to the file tag or in Roon does not change that.
Highly annoying. See here: