country/region error on sync'd iphone

My music library is about 160GB. I purchased the 256GB iphone 11 to accommodate the entire library. I don't want Apple Music. I don't want cloud music. I just want to transfer music from iTunes to my phone. Period.

A 'helpful' person from Apple ran me through a number of steps which ultimately caused me to have to delete all the music from my phone and then spend about 32 hours resyncing. I move my entire library to a new (Windows 10) computer, resync'd to the new computer, and all was well. I thought.

For no apparent reason, I'm not getting "This song is not available in your country or region" errors for random tracks on my phone - many (most?) of which were actually ripped from CDs through the years. Others are MP3 files purchased from Amazon. None of these came from anywhere other than the US.

I changed the country/region in my phone settings to the United States, and REentered all my credit card/address info.

Trying to sync the phone and I get a goofy error that "this iphone cannot be sync'd right now. unknown error."

I should also add that some of the songs on my phone (when viewed in iTunes) have the dreaded dotted gray circle next to the titles, but play on the phone.

So what do I need to do to simply copy my songs to my phone. That's all I want.