Unable to download or listen to music offline on my iPhone

I have an iPhone 16 pro, and it's updated to iOS 18.2. I have a current subscription to Apple Music. I was using Apple Music to sync my music library across my devices (iMac, iPad, iPhone, Macbook). Sometime in November, it stopped syncing all of my music and playlists (in a seemingly random order). My favorite playlist, which I created originally on my iPhone but synced with all my devices, disappeared from every device except the iMac (OS Sequoia 15.1.1). I don't mind on that I don't have all my playlists on my iPad or Macbook because I don't usually listen to music using those device but it aggravates me to no end that I can't listen to that playlist on the phone.

Also, Apple Music is behaving oddly on all devices except my iMac. It won't allow me to download music or playlists to my device (including music that I've actually purchased) and I can't favorite playlists. I notice that on my devices (aside from the desktop) that I have two libraries in Apple Music: "My library" and {My name's} library. It defaults to My library and I literally have to fight it to select the other library. That library seems to have the missing music and playlists - however - it won't stick and always reverts to "My library." I unable to download content from either library.

Steps so far:

Stopped syncing my music library (turned it off on iPhone and desktop).

Deleted the Apple Music app and related data from my iPhone.

Did a reset/force quit on the iPhone then powered it up again.

Downloaded the music app again

Went to settings>apps>music and checked sync library on both my phone and desktop. No joy, still had my whole library on the desktop and missing songs and playlists on my phone.

Repeated the whole process again, except this time I didn't select sync library on my iPhone. Instead I did a manual sync. This worked and the content and playlists I selected now appear on my phone - if I've selected "my library." It stills shows two libraries and the one with my name, doesn't seem to sync with the desktop. If I select that it shows an incomplete list of songs and playlists (and I still can't download).

I realize I've written a novel, but this is making me insane.

One more datapoint: on my desktop I located my music library database. The current one is 4.4 MB. When I checked the previous libraries folder I noticed there was one that is 77 MB and was last modified on 11/11/24 (about when I started having problems).

Thoughts? Solutions?