I don't have any numbers on this, but I'm certain lots of "flat-eathers" are just trolls that enjoys annoying people who tries to act smug and smart, but in actuality failed to get the humour behind the flatness of earth. Anyone who is seriously trying to argue with flat-earthers have a very low bar for intelligence. Which is not to say that there aren't actual dumb people who actually believe the earth is flat, but I reckon those people are far below the minority.