You’re right, Plex doesn’t use the Composer or conductor tags, and @BanzaiInstitute’s advice is good. I’ve had the same battle with Plex, and I created a feature request asking for support of tags that are necessary for classical music. That post also lists the most relevant tags, and which of those Plex does and doesn’t support. There’s also a request specifically for the Composer tag which would be the bare minimum necessity.
Until (if) that happens, my solution has been to create a library for Classical, and another library for everything else. I think the same as you, the artist is the orchestra and the album artist is the composer, so that’s how I tag them. Albums with multiple composers are simply going to end up as “Various Artist” albums, so I have a “Various Artist” artist in Plex that has all those albums. It’s not ideal, but ideal won’t be possible until Plex implements the bulk of my feature request.
