Many (but not all) of my song files are missing

Something like 90% of my music is still listed in my library, but can't be played because Music shows an error ("...because the original file could not be found"). When I search my Music folder I don't find any files; there are folders for the relevant artists and albums, but they appear empty.

The library is 8K-10K songs collected over the last 15+ years, a mix of iTunes purchases, CD rips, and files downloaded from elsewhere (e.g. Bandcamp). There doesn't appear to be any pattern to what music is missing or remaining.

I have read several similar questions, and I have tried the steps in Empty/corrupt iTunes library after upgrad… - Apple Community . I can't find any older library files (.itl files) and the old iTunes Music folder is where I'm finding the empty folders described above. I've tried to restore the Music directory from a Time Machine backup, but I'm not seeing much success there.

In mid-January I had to restore the OS on this machine, which is when the trouble started. I've been able to recover all other documents in my user directory except the music. Is there another place I should be looking?