Apple Watch has torpedoed my Tunes

I bought an Apple Watch Series 6 today. I set it up and charged it. Went to open my Apple Music to transfer some tunes and now get the infamous "This computer is already associated with an Apple ID" message. Let me be extremely clear:

AT NO TIME IN THE PAST TEN YEARS HAVE I EVER USED ANY OTHER APPLE ID.

None. Ever.

I am not part of a family plan, or any kind of sharing. But out of NOWHERE, suddenly my music is completed fouled up.

On top of everything else, now some of my song titles have been replaced with random strings of numbers.

How do I fix this????