Why do you say the Earth is proven to be flat? I think we have had proofs since ancient times that the Earth is round. The Earth is often represented by a sphere as that is a very good model, but it is in fact a kind of squashed sphere shape, and of course just loads of bumps and dips like mountains and valleys when you look at the surface up close.
We’ve known the Earth is a sphere for thousands of years. Now we know it’s more of a distorted oblate geoid (but this is still a sphere to anyone looking with their eyes, it’d definitely not flat!).
This is a video taken from one of our spacecraft shortly after it separated from the rocket. You can clearly see the curvature of the earth.