Sync music between PC iTunes and iPhone Music isn't working

I have just installed the most recent version of iTunes. I have verified I'm using the same apple ID on my phone and PC, and have logged out and back in to iTunes several times. My phone is connected via cable.

in iTunes, under Edit > Preferences, I have turned on iCloud Music Library. On my phone: Settings >Music, "Sync Library" is turned on.

However, nothing I do synchronizes music from my PC to my phone, and I have tried Sync several times.

I've seen guidance to go to File > Library > Update iCloud Music Library, but it is greyed out.

I've also tried removing and re-adding music that refuses to sync. (Note the same album syncs to my daughter's iPhone just fine)

What else am I missing? We have the same phones (iPhone 16, but my just-replaced iPhone11 had the same issue) - the only difference is that I am the account owner for our Apple Music subscription if that matters.

Help please!!