Screenshot on iMac not working

Make sure the Screenshot is saving to your desired location when presented with the "Options" choice:

Take a screenshot:

"Where to find screenshots

By default, screenshots save to your desktop with the name ”Screen Shot [date] at [time].png.”

In macOS Mojave or later, you can change the default location of saved screenshots from the Options menu in the Screenshot app. You can also drag the thumbnail to a folder or document."

Review Take screenshots or screen recordings on Mac, and thoroughly describe "not working."