Please do not waste your time thinking that the earth is flat.

If you want to investigate the truth, read the original text of Galileo and Newton.

A very good book is

"Big Bang: The Origin of the Universe" by Simon Singh

He explains very well and simply how the ancients (Eratosthenes, Hipparchus and many ohers) were able to calculate the radius of the Earth, of the Moon, of the Sun and their relative distances.

The conclusion is: dismiss any theory about flat earth because even the ancient Greeks knew it was not and were able to prove it.