Music Assistant gains an option to synchronize a Plex music library when Plex finishes scanning new content. That avoids waiting for the next scheduled synchronization, which runs every 12 hours by default. RyanAtTanagra saw a newly added album appear about 20 seconds later in a test with a real Plex server.
The “Sync when the Plex library changes” setting checks that the library’s contents actually changed before starting work. It reconnects if the notification connection drops, while the regular synchronization schedule remains in place.