My songs will not transfer unto my iPhone. Error is song not available in your country or region.

I own an iPhone 13 pro max. I have a few songs on my PC (iTunes) pc that plays ok, and has done the same on my iPhone until I updated my software to IOS 18. I now get the error message "is song not available in your country or region." The majority 99% are songs i ripped from CD a few years ago.

I am able to play the songs on my PC via iTunes but it does not synch to my iPhone.

I have delayed buying the iPhone 16 as I refuse to invest in another iPhone until this issue is resolved.

Help!!