Unable to get my MacBook and iPhone to sync music

Hey. I have an iPhone 13 & a MacBook Pro mid 2014 running MacOS big sur 11.7.10. No Apple Music subscription. I’m having great difficulty syncing music from my MacBook to my iPhone. Last year I did it fine but now when I am able to transfer it syncs my whole library but weirdly, not any music that has been on the iPhone before. Sometimes it comes up with an error messages saying those songs can’t be synced because the phone already contains the songs in that playlist. The phone seems convinced that these tracks are already on the phone when they are not accounted for in storage & I’m not able to access in music. Is there a way to reset this?

I’ve already tried deleting & reinstalling music on my phone a couple times. & opening music with option & command buttons held. Every time music syncs it syncs less music so it’s getting worse.

is factory reset worth a go?

thanks.

[Re-Titled by Moderator]