Grayed out songs in Music

I had about 900 songs in Music on my iPhone X that I manually uploaded from iTunes in a 2011 Mac mini. The process is a little clunky; adding songs sometimes would take more than one time and turning both devices off and on, some songs are taken out of playlists, or grayed out, etc.

I regularly add songs I got from radio stations Song of the Day websites, my own CDs, and the old iTunes' Song of the Week, which is legal and should be compatible with Mac products. But today was the day in which all songs went gray or didn't appear on the phone or on the iTunes screen for the iPhone.

Some forums say that I should sync, but that didn't work, and I DO NOT want all the same music in all devices; I don't want to listen to the same songs at home, in the office, or while walking.

I guess I will have to manually delete all the grayed out songs from the iPhone and reloaded on iTunes.

Unless there is better advice.