iTunes not syncing with iPhone

I have a lot of my own personal music and downloads of MP3's in my iTunes Library. When I try to sync my iPhone 15 with my computer's music library, I get the following message:

“This Song” could not be copied to the iPhone “Thomas M Stafford’s iPhone” because an unknown error occurred (-3234).

At this point, all syncing stops and I'm left with only about 300 of the over 5,000 songs in my library not on my iPhone. This error stops any further syncing of songs left in the cue.

It is never the same song. It's always a different song which is why I changed the message from a particular title to "This Song."

Please advise. I use my music for performances, and it's awfully cumbersome to create a file in my iCloud to manually access for performances.

Thank you for any help or advice.