So the biggest evidence that the Earth is round is that you can fly around it in an airplane. Like for $1500 USD you could buy a plane ticket around the world, and you could see for yourself that it's round.

If you still think it's flat, then you're forced to entertain the absurd notion that every pilot who has flown around the world has been "in on it," and that every air traffic controller has also been "in on it," and probably many others as well. We're talking about millions of people throughout history.