If you are really interested in the flat earth idea, you might try explaining why the sun moves across the sky in a circle that is parallel to the ground, and never falls down, in violation of multiple laws of physics, which are known by observation, such as:

1. Objects fall to the earth.
2. Objects do not move without something pushing them.
3. Objects that are moving through the air move in a straight line (measured along the ground); they do not move in a circle unless you are talking about a boomerang, and even then not really.

If you don't believe me, just pick up a rock and toss it. Does the sun move like that in flat earth theory? No, not at all.

You might also try to explain why it moves in a spiral while you're at it, according to the annual cycle. Each day it moves in a circle of slightly increasing radius. Why? And at the solstice it reverses the direction of the spiral. Again, why?

Or draw a map of the earth, drawn to scale, that shows the relative position and shape of every geographical place. No flat earther has ever done this either. The reason is that it is not possible to draw such a map that would accurately reflect the known distances between places on this earth.

Flat earthism isn't really a theory, properly so called. A theory attempts to explain observed phenomena in a manner consistent with known information. Flat earthism simply starts with a bizarre assertion and then assumes there must be some explanation for everything that doesn't fit the theory.