I use "DS Audio", the web/native app that comes with Synology home NAS. It works pretty well. Probably not as well as Plex or Jellyfin. Has anyone used both?
Both of them are surprisingly good in a lot of ways, but also...kind of ugly. Not enough so to not use them, but I wish these two apps had the same UI polish that some of the other first-party Synology apps have.