Songs disappeared from Music/iTunes

More than half my songs have disappeared from iTunes/Music/whatever they're calling it today. Some were ripped from CDs that I no longer own, others were purchased from the iTunes store. I've been a Mac user since 2002 and bought my latest MacBook a few months ago. Browsing this forum, I see that there is a known issue regarding Apple Music scanning your existing library for items that can be streamed and offloading those titles to save space. I didn't take them up on the free trial, nor did I ever sign up for the paid extension. Still, this seems to have happened to me because I got a pop-up warning me that the "trial period" was coming to an end and I was losing the chance to extend it. I simply ignored the message and went about my business, not thinking anything of it since I never utilized the streaming service at all. Today, I opened my Music app to listen to one of my lovingly, thoughtfully prepared playlists and THEY ARE ALL GONE! Not only that, but my library is about half the size it was the last time I used the app. It took a minute to stop panicking and locate the files on the hard drive, but they're all still there but for whatever reason, the Music app will no longer recognize them.

How do I get the Music app to start seeing them again? I've spent 45 minutes digging around the menu and on this forum with no luck. HELP!!! They're all in the same directory they've always been in, right alongside songs that Music *is* seeing, so clearly this is a selective thing.