Here is my problem with the flat earth community. It's fine to entertain all ideas, but at a certain point you need to perform experiments to test your hypothesis. The earth can be proven to be round, and you can even calculate its circumference simply with two sticks far apart. All you have to measure is the distance between the sticks, height of each stick, lengths of the shadow created, and angles of the shadows created. Some basic geometry and trig relationships make the calculation rather simple actually.

Another easy way is to get a boat and try to navigate with triangles and planar geometry. FYI: you will get extremely lost. There is a reason we invented trigonometry, and it wasn't just to fool everyone.