Unable to sync my MacBook Pro music library with iPhone

I have a strange problem that seems to be above my pay grade. I've been receiving error messages when syncing music between my music library and my iPhone. Equipment is a MacBook Pro 2013 running OS Catalina version 10.15.7 (19H2026) and iPhone XR, iOS 18.4.1.

The error message indicated that XYZ file was not copied to the iPhone “Name iPhone” because it could not be found. When saved the text file showed about maybe 12 to 15 files that could not be found.

These files were either MP3 files or video files I used a few years back when creating videos in iMovie. The videos may have had the audio stripped and added to the soundtrack. The files are no longer a part of my present music library, nor are they on my iPhone. I was able to locate the files on older Time Machine backups and add them to the library thinking that would fix the problem. When syncing the music library to the iPhone I continued to receive the error message.

Relying on career troubleshooting experience I created a new blank music library and tried to start from scratch. When I connected my iPhone to my Mac and sync'd the library I received the error message again despite the fact that both the music app and the iPhone song list were blank. When I selected the Sync Settings on the Mac music app for the iPhone and selected the Movie tab there were 16 items. I could either select to sync them all or individually.

I believe these files are creating the error message, but I have no idea were these file live or how to delete them. Any help and suggestions to correct this problem would be appreciated.

[Re-Titled by Moderator]