Sync issues Mac to iPhone Music

MacBook Air M1, OS 14.2.1. iPhone 12 iOS 17.2.1.

I cannot sync my Music library from my Mac to my iPhone. It backs up OK but then says "preparing to sync" this goes on for hours, even if I only select one song to sync.

I have tried to sync the same songs from my Win10 PC using iTunes, same result.

I have used 2 different cables to connect and tried different ports on my Mac, same result.

I have deleted all the existing songs from the iPhone and tried again (and again etc), same result.

I have reset the iPhone to factory defaults, same result.

I do not have an Apple Music subscription, and only the basic 5GB iCloud storage so can't transfer that way.

Help? Rob.