You’ve solved it by now but this Jellyfin doc article was helpful for me, beginning with the section Naming.

jellyfin.org/docs/general/server/media/movies/

There at similar guides for TV Shows, Music, Books and other mixed media.

There are also guides for “stacking” multi-segment media titles, for example Lord of the Rings movies which come on several discs.

Jellyfin can be a bit opinionated about detecting bad metadata. The override tags in the media data filename or folder name can help clean that up. In fact, I’ve started hard-coding those [tmdbid=…] tags in my encoding workflow because I’m just so damned tired of fighting with the metadata feature.

Hope it works form you,.too.