Serious flat earthers believe the earth is the "basement of the universe." It spreads outwards from the north pole; Antarctica is not a continent at the bottom of a ball but a ring ice wall around the "Earth pond." The ice wall is 100-200 feet high in general and contains the world's oceans. It is unknown (to normals, anyways, perhaps the world governments that signed the Antarctic Treaty know) how far the ice plateau extends once you ascend the ice wall.Does it mean that someone could get on a boat and head in any direction stay on that heading and when confronted with a land mass, simply go around it to get back on that same course and then one could endlessly continue in same direction and never find the end of the earth?
If we are under a dome then there is an end eventually. Actually, now that I think about it, the Bible says there are ends to the Earth, but we don't believe in an edge you can fall off of into endless void. Earth is not a cracker floating in the heliocentric model solar system.