Yeah, multiple genres would be nice. Of course, in principle, it’s no problem to correctly tag ALAC files with multiple genres, but iTunes just shows them as a sub genre. I always have some “test files” to see how the software reacts. For example, I have tagged Dave Grusin’s film score for THE FIRM with the genres “score” and “piano”. On my music server I find THE FIRM under the genre tags “score” and also under “piano”.
(I have also have Max Richter’s HOSTILES both as FLAC and ALAC in my collection, just to see immediately if and when any software/music sever would treat a FLAC any different from an ALAC.)