Reminds me of Galileo being prosecuted for defending his belief that the planets revolved around the sun (heliocentrism). The earth isn't flat, but turns out the universe is. One would hope that would be enough for them.

I was gonna say they could look at a photo but I'm assuming that if were the case they wouldn't be flat-earthers.

I mean despite them being able to use telescopes and seeing other spherical shaped planets.

The North Pole is the answer I've seen given. At least some of them believe that the azimuthal equidistant projection map on the UN's emblem is what the world really looks like from above