If the Earth is flat, then the Sun would have been visible from the entire Earth, but that’s not the reality. So, to rescue the concept of the flat-Earth from being falsified, they invented an ad-hoc hypothesis that the Sun appears to set because of perspective and refraction.
Zooming in using a camera merely magnifies the center portion of the image. Changing zoom does not change an object’s position with respect to another object or the camera. It will not reveal more of a distant object.
Flat-Earthers often claim that zooming in will reveal distant objects that are ‘allegedly’ behind the curvature. They are wrong. If the object is really behind the curvature, then no amount of zooming can bring the object back into view.
Light waves are not always moving in a straight line. When it passes through a medium of a different refractive index, the waves will deviate. The phenomenon is called refraction and described according to Snell’s Law.
Earth’s atmosphere has variation in air density that depends on the altitude. As the refractive index changes with the density of the medium, light waves passing through Earth’s atmosphere also experience refraction.
We know for granted that during an equinox, the Sun rises from the east and sets in the west. Such facts are undisputed and have been verified through centuries of observation.
The flat-Earth model, however, is unable to accommodate this simple fact. And thus, it is not hard to conclude that the flat-Earth model does not represent reality.