How do you change the desktop picture with OS Monterey?

and yet another option is to open your photos app, single click on one of your pictures and click on the "share" button that's on the toolbar.

and then, in the dropdown menu, choose "set desktop picture"

System Preferences > Desktop & Screen Saver > Desktop. Choose something.

You can also just right click on the screen and click "Change desktop background"

sorry I first "pointed" to the wrong button for the "share" button on the photos app toolbar. I have corrected it in my previous reply.