What if the underside of earth had stuff down there?

That's where you get a lot of the real 🤯-tier pseudoscience and pseudohistory.

Dinosaurs and lizard people are down there. Nazis and Communists are down there. Mole people. Atlantis. The Garden of Eden. The sky is the limit.

Yeah, that's how I've seen them describing near-equator orbits more than once. (Back when the entire thing was an internet joke, the models were very funny.)

It's polar orbits they have an issue with.

This is because flat earthers don't understand anything about science or physics or basic common sense and as a result believe the most insane things.

They spend their entire time trying to come up with increasingly convoluted ways that a flat earth could work, rather than just accepting that the simplest explanation is that, in fact, isn't flat. Their explanation for why you can't see mount Everest from the top of any reasonably high hill anywhere else on earth, involves throwing out all scientific thinking back to Aristotle and starting again, don't believe in geometry or infinitely parallel lines.

According to flat earth supporters, if the earth were moving in any way at all you would feel it. Since we don't feel any motion obviously the earth is stationary