Recent iPhone Apple Music error. ~Songs not available in my country or region.

Recently upgrade from 14 Pro Max to 16 Pro Max. I also tried (almost forced) to try the Apple Music and Apple Devices apps. Somewhere in this process, I believe, am not getting a "This item is not currently available in your country or region." error message in the iPhone apple music app on SOME (~80%) of my songs. I have a VERY large music library and can no longer used the Apple Music app for listening. I really have NO IDEA what happened or how to correct this. I have tried many things (restoring/transferring from a backup, etc), to no avail. My desktop windows PC's iTunes doesn't show any library items within the "Sync Music section. I am BAFFLED. I'm willing to pay for a solution here!!!! Thank you, Dennis