Let’s travel in one direct across a flat earth, without moving up or down or sideways moving in a straight line where would a person end up, most certainly not at the same place they began like on a sphere earth. On a flat earth you would reach an edge and would have to make a directional change either left or right or over and under the flat earth and that has never happened no one has ever had to changed their direction to end up at the starting point around the sphere earth. there’s no edge, the earth is far as the east is from the west which is pretty far, move east and you will always be moving east.