Full screen screenshot shows two neighbouring screens in one workspace for just one monitor, one of them an empty desktop

Could it be that Linux thinks by default that there is a second monitor, even if none is attached? I might also have forgotten about having changed the settings myself long time ago. When I'm pressing the PrtScn ("Print Screen") button, it's taking a screenshot of two screens that are in the workspace, one with my opened applications that I see on the monitor and one empty desktop. When I check the workspaces with CtrlAltUp, I see that I am in just one workspace, the other three are empty. Strangely, if I take a screenshot again now that I played around with a WLAN connected TV and switched workspaces / virtual desktops with CtrlAltRight/Left randomly, and after adding more applications, having many applications opened, I get only the one screen that I am looking at in that screenshot - this seems to work now. I do not know how to get back the error in question, but I know that I had it for many months so that I could not use the built-in screenshot app at all but had to change to flameshot. One could say that this is fixed without knowing why, but I leave this question opened so far until it gets closed by votes. There might be other users with the same problem. I have Linux Mint 20.04, but I think that this is a question for any Linux OS.