Or Flat Jupiters, maybe. I'm imagining a space station with a large population orbiting very close to a gas giant. The horizon stretches away in all directions and an infinite variety of cloud patterns wiz by below. Some individuals get it in their head that they are flying over an infinite flat plane rather than going around an impossibly large sphere. Assume that, like modern Flat Earthers, they reject information from authorities outside of their social circles and measurements from equipment they can't use themselves. These people also wont or can't (perhaps for economic reasons) leave the space station to view the planetary system from a different vantage point.
Is there something about their situation aboard the station that would make it plainly obvious that the planet they orbit is spherical and prevent this idea from spreading?