Not sure this actually works for a music library - at this moment the server is busy updating the metadata for my music library., as can be seen in the image below. (“The Book of Secrets” is an album by Loreena McKennitt) All of my albums now have only one genre -.a very disappointing result even though I thought I was minimizing the damage until Plex fixed the issue.
The update local metadata option has been turned off for almost two weeks, so Plex is basically confirming that all of my tracks have only one genre right now. 
EDIT: this also affects the genres available for the artist and album. Since only one tag is read from the embedded metadata in the individual tracks, the genres are reflected at the artist level. Plex used to amalgamate the genres from the tracks at the artist and album level.
Difference is obvious on this album. First image is from Dec 21, 2021, with 15 genres. Second is from today with one genre. I can’t imagine smart lists, genre radio, etc working with any sort of decent results.
