National Geographic had a segment about the Flat Earth movement. The ten-minutes piece begins at about the 11:30 mark.
What surprised me is that it said that 2% of the American population believes in it. That works out to about 6 million people and is said to be growing. The other thing that disturbed me is that there seemed to be a lot of young people in the group. The video shows a small model of a flat Earth.
I got the gut sense that although many of the people in the movement are true believers, Mark Sargent, the leader of one main faction (the side that believes there is a dome over the flat Earth and feuds with a rival group that says there is no dome) did not really buy it but was enjoying the ‘game’.
The film crew took some flat Earthers including Sargent to a demonstration to recreate the observations of the Greeks over 2000 years ago that was one of the pieces of evidence that convinced them that the Earth was round. It is how a boat slowly sinks over the horizon. But the flatters were not buying it. I could have told the film crew that it would be useless. No single piece of evidence will ever convince a determined skeptic that what they believe is false.
What I found interesting was that for some reason these people seemed to feel that a flat Earth implied the existence of a supernatural power and they took comfort in that. They also felt that the round Earth was being promoted as part of a large-scale conspiracy by a shadowy powerful group and that scientists were part of it.
So you can see how this would appeal to other anti-science groups like climate skeptics, anti-vaxxers,, QAnoners, and intelligent design creationists, all of whom think there is a vast conspiracy to hide the truth that only they possess.. I would not be surprised to see a large overlap between the memberships of these groups.