Question - How does this capture the entire screen, except its own window? I've tried making similar functionality in Python to add visual effects to the scree

Question - How does this capture the entire screen, except its own window? I've tried making similar functionality in Python to add visual effects to the screen, but the only way I found is to use one of the packages which leverage the Screenshot functionality. But this causes recursion since my app's window will be in the screenshot (unless I put my app on a different monitor or a different area of the monitor). How do they avoid that?