GPS technology wouldn't work as well as you think it will if the Earth is flat. It's a sophisticated tool that uses satellites to triangulate positioning along with the consideration of the planet's curvature. Also consider astronomy and centuries of celestial body mapping of the skies above. If you think the many space apps we have are all conspiring to trick your intellect, try getting hold of a telescope and do your own research. You'll soon find that the Earth is a sphere.
I've done this in university, even manually calculating positions on ground and in-space using basic geometry. So no, Earth is not entirely flat like a paper map spread wide on the table. It's a sphere made up of many flat planes. That said, I'm actually okay with conceding that some of the many things people believe cannot be disproved (or even worse in my case, cannot be proven).
After all, there are conspiracy theories which have over time, proven to be true. So yes, I don't necessarily have strong positions against every bizarre claims although I do, especially if claimants cannot prove their claims satisfactorily. Personally, I'm not even ruling out stuff like alien overlords. But for god's sake, the earth is not flat. It's not even a belief (excluding the default belief required to trust our own thoughts and senses). It's something that anyone - all 8 billion people in this world - can study and actually test the calculations out for themselves.
Image from Wikimedia.
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