Flat earthers claim we can see too far for the earth to be a sphere. They actually never test it. They also miss the elephant that for flat earth you cannot ever see far enough and bottoms of distant objects are obstructed, contrary to all known behavior of light.
Chicago Skyline from Michigan
A photo of the Chicago skyline taken from Grand Mere State Park in Stevensville Michigan shows the skyline of downtown Chicago.
Flat earthers claim ridiculous amounts of predicted obstruction, never bothering to include the observer’s height. They also tend to get sloppy on the distance. The observer was 180 feet above the water and the distance to downtown Chicago is 53 miles.
When analyzed using an earth curve calculator that has the capability to adjust for common conditions near water, the predicted hidden if the WIllis Tower is about 300 feet. The tower is 1450 feet tall. There is no problem at all with the observation on a globe.
However, the bottom of the city is obstructed by the water. Either Chicago is flooded, or the earth is not flat.