Can't access music on the iTunes app or Apple Music app on new computer. Never set up an Apple ID.

My boyfriend just got a new computer. He has 28,000 songs on iTunes. I moved all of this music from iTunes to the new computer. (backed up first then added folder to library on new computer's iTunes app) This worked as it should and all the music was there on the first day, but now it is not.

All of his his music came from outside sources. He had never set up an Apple ID.

Today, when I open the iTunes app on his new computer, a popup appears with the following message:

"Your music, movies and TV shows are now available in the apple music and apple TV apps"

But since he never set up an Apple ID, I can't access any of his music through Apple Music. And I can't access the music in iTunes because the music had been moved to Apple Music. When I try to "add folder to library" in iTunes, it asks if I want to add his music as an audio book.

The old computer still has his music on the iTunes app. But not on the new computer.

Can someone please help with this?