Newly-created Playlists Will Not Sync

Suddenly (it always is, isn't it?) newly-created playlists within the Music app on my iMac are not syncing with my iPhone. By that I mean not just that tracks aren't listed under a playlist, but the playlist itself does not appear on my phone. The music syncs just fine from my iMac library to the phone, as well as older playlists. Just not any new ones.

I spent close to three grueling hours with Apple support (both chat support and live on the phone), including not less than 6 different support staff. In the end, Apple said that with the new Big Sur operating system, newly-created playlists on the iMac Music app will not sync to a phone unless I subscribe to either iTunes Match or Apple Music.

I'm skeptical, as nothing in the help articles even suggest that, and particularly as already-existing playlists on my iMac that I update with new tracks do sync with my phone; i.e., tracks newly inserted into a playlist on my iMac also show in the same playlist on my iPhone. So, playlists do sync in Big Sur, but I can't figure out how to get newly-created playlists on an iMac to appear on my iPhone.

Well, happy to hear any insights.