This worked! Thanks!
From my experience, the Recents aren't so much "stuck" as they appear to be in a backlog. Using the suggestion from mrmax1986, I just kept adding the same song to the top playlist in the three "Recents". That top playlist would go away, and then I'd add it to the next playlist that rose to the top of the three "Recents". Sometimes one of the playlists would reappear, but that is simply because the playlists can be in the backlog multiple times (at least this is how it appeared to me). My Recents had been "stuck" since Dec. of 2023 (four months), so my backlog was VERY long. I think I added my song to over 20 playlists before the Recents FINALLY started showing playlists that were actually recent... if the playlist you are adding to keeps showing up in the Recents, that's a good sign you finally got to the end of your backlog.
One note: when you add a song to a playlist, in that latest iOS after you add the song it appears at the bottom of the screen for a few seconds; if you tap on it during those few seconds, the playlist will open and automatically scroll to the bottom of the playlist... where you can then remove the song if you really don't want it there (which was true for me, as I was simply using the one song to help me clear this backlog; I didn't really want it in all of those playlists).
