A week ago I dropped my notebook on the keyboard of my Mac and two squares appeared on the desktop and they simply don't go away. The Mac function perfectly but It looks like it has two masks and its just annoying I tried reseting and closing the finder but it didn't go away.
Mac mini (2018)
"I dropped my notebook on the keyboard"
That's a very strong clue. The images look like incomplete screen prints as mulberry58 alludes too. But having been dropped, I suggest you take it to Apple to be evaluated.
Does changing your desktop picture have any effect?
If you have been trying to make a screenprint, something like this sometimes happen. Does is disappear when you reboot?
strange square appear on desktop
