The edge is composed of ice and tundra. It encircles the disk and holds the oceans in. It is what sphereists call “the south pole” or the Antarctic “continent”. So why hasn’t anyone been to the edge? You have to remember that atmosphere functions differently on a Flat earth. Earth is not a ball that that magically glues people and atmospheric gases to its surface. The ring of tundra and ice that encircles the earth extends outward for many thousands of miles. Before you can even “see” the edge, oxygen levels become less than those at the summit of Mt. Everest. Any attempts to reach the edge would necessarily end in tragedy.
Well, why don’t we just fly there or send a probe? Good question. Just as oxygen and temperature decrease the closer you get to the edge, the interaction of earth’s atmosphere mixing with the atmosphere of space (yes, space probably has an atmosphere of some sort) causes violent winds that would make any such attempt futile. Of course, perhaps the government has “seen” the edge. But it is doubtful we would ever hear about it given the 18 billion dollar budget NASA regularly receives and that fills the pockets of an elite few.