My "iTunes" Is Messed Up -- How Do I Build a New Library Using The Songs On My Hard Drive?

No idea how but my (what I used to call iTunes) is messed up and doesn't show any songs, or playlists, or ... since January 2020.

But the songs exist on my hard drive.

How do I "Start From Scratch" and build a new Music / iTunes library using the songs on my hard drive not the stuff in the app?

The "most recent" song in the app (when sorted by "Date Added") is 2020-01-22

But on my hard drive "My Music & Photos / Music / iTunes / itunes music / music" there are tonnes of recent albums

So how do I get rid of the junk in iTunes and build new using these songs on my hard drive?

I'm running:

Music 1.0.6.10

macOS Catalina 10.15.7

On a late 2014 Mac mini