Recent photos are missing from my iMac

RECENT PHOTOS ARE MISSING FORM MY IMAC. THEY WERE THERE A FEW DAYS AGO. I sat down today to continue to edit photos from a recent trip on my iMac (running on macOS Big Sur 11.7.4). Sadly, the photos are gone. They are not in the Trash. I'm thinking it has something to do with icloud or photo libraries (which I totally do not understand). I'm an entire idiot when it comes to computers despite using them daily for forty odd years. Any idea what to do?

[Re-Titled by Moderator]