OK, I downloaded another screen shot application, and it got me to an area that isn't obvious - You'll see nothing selected on the left side, but on the top right, it shows "allow the apps below to record the contents of your screen..." Once the new application showed me the location, I was able to drag Skitch to that same screen, and it works now. This might be a Big Sur issue, as selecting the app to record the screen is not possible unless the system is aware that it needs to be available/shown.