music releases on YouTube are in fact releases now, and also I’ve seen still-image videos added as releases as well (these are usually treated the same as YouTube Music™ releases, as @tigerman325 mentions above, being entered the same as audio releases)
I believe the Releases tab comes from YouTube Music™, which is YouTube’s music streaming outgrowth (and has to be distributed to like Spotify, Deezer, TIDAL, etc.). I don’t see a way to add it on my personal YouTube channel
we’re currently working through the guidelines on what music video releases’ place is in the database, if you’re interested