Earth’s shadow on the moon during a solar eclipse is circular. If the earth was a flat the shadow would have a different shape like a line perhaps, no? Wouldn’t you expect the gravitational force (or whatever they want to call the force typically associated with gravity) to be different away from the center of mass of a flat Earth? We don’t see that being the case, so we can surmise all of the surface of the Earth is at an equal distance from the center of mass, suggesting a spherical shape.