Sync error 256 been going on for a year!

OK so for about a year my Iphone 14, which I keep up to date with software, and my 2019 IMac on, currently, Sequoia 15.3 (which I always update ASAP) have not synced. I have found that if I wait for the back ground Finder to finish it's sync, then hit Cancel on the error message, it 'kind of" works IYKWIM but it is frustrating.

The message I get is Error 256 but I can find no reference to this anywhere. I even chatted to Apple Support for an hour and they could not help. I have done all the obvious things - changed cables, reset and restarted devices, deleted all music off the Iphone, etc multiple time but still I get this message (attached) every time.

Anything else I can try please? Thanks