The only things I can get rid of (or that I want to get rid of) are some of the documents and downloads. I finished the music. There are no movies. Just a few family and pet pics. Some are easy, but some have to be clicked on to even know what they are. That's what's tiresome and boring. It took awhile then I stopped at the "e's". I'll pick up again tomorrow. Thanks, Artie. I guess there's nothing that shows up in my Disk Utility that I can ditch, right?
Disk Utility shows you your OS structure, not its contents. There's nothing you can see there that's a part of your problem.
I'm pretty sure you've got an external drive, so if you can't trash enough data to complete your Monterey upgrade, you'll have to park some stuff on it at least until you're done.
Hmmm... Take a look in your applications folder and see if you've got a Monterey installer (maybe "Install macOS Monterey"). If so, it's around 12 GB of your problem that can be overcome by moving it to your external, deleting it from your internal, and booting into and doing the installation from the clone on your external.
It would be ironic if the installer, itself, is preventing you from installing.