I'm sorry Joe, as you might recall, Windows is not my standard OS. I just tried copying an image on MacOS into clipboard, right-clicked into a new Paint document on Win 10 and it successfully pasted. So try right-click on Paint document and choose paste.

I copied image to Win 10, opened with Photos and copied into Clipboard but paste did not work. Perhaps try copying it using Photoshop instead.

Another option is to right-click the image file you wish to process with Paint and choose "Edit with Paint".