One of the simplest proofs that the earth is round and is certainly not a flat disk is the fact that sunrise (or sunset) is at different times at different places throughout the 24 hour day. That requires a spherical or cylindrical earth. The latter can be discounted by the fact that the duration of daylight hours is different for each location on a line of longitude.
Ask a flat earther to construct an earth that could exhibit both of these phenomena.
