Screenshot not working

I'm revisiting this problem (screenshot freezing) that was posted some time ago by a user experiencing the problem after an update to Mojave. I experienced the problem back then too, and still have the problem. I'm running Catalina on a Macbook Pro (2019). Here is a quotation from the OP:

"If I use it, when opening up the normal 'location area' appears; when I have adjusted it to the area required and hit Enter, the footprint of the 'location area' is visible against a darkened background and this footprint and background won't move.

I can operate the content shown on the darkened screen, but am unable to remove the footprint and return the screen to normal.

The only way I seem to be able to recover is to either restart or log out and back in.

Has anyone any experience of this or any suggestions on how to overcome it please?"