There are a lot of variables here. Plex, in its default configuration, uses the folder/filenames of your files to identify your albums, and match them with an online database (Musicbrainz) to get metadata, which Plex stores in its database. If there are tags embedded in the music files, they may not be used in this configuration.
I don’t tend to pay much attention to that case, because I’ve found that the online databases have too many errors for my liking. I’ve put in the work to perfect the embedded tags in my files, and have configured Plex to prefer them over online sources. If your Plex server is configured to prefer embedded tags, the article at that link shows what you need to do. But keep in mind that your embedded tags must be very accurate in order for it to work.
In either case, the folder/file structure is important. This guide can help:
