Yes flat means straight.
The answer is we simply cannot see that far. Pollution/water/dust/sea salt etc all will hinder view over long distance and it just becomes blurred.
The centre of earth is our “nth pole” with the star polaris above and everything circling around (google star trail photo) This is another “proof”’of everything revolving around us and not the other way around. All compas’ point to the magnetic north pole. I’ve heard some people speculate that the Garden of Eden or the Tree of life is there.
There is no south pole, antarctica isn’t a blob of ice at the bottom of the ball, it’s an ice ring holding all the oceans in. That’s why if you go south from any direction you end up at the antarctic shore line or wall.. look into cpt cook or admiral birds description of the south of our world, futher more read about operation fishbowl or high jump.
Time zones are different because you are still imagining a giant fire ball in space, think of the sun as much smaller and local and only lighting the lands below it.
Think about this, people circumnavigate the world (or used to) everyday, but only east-west or west-east.. the reason you cant north to south is because of the ice ring (I’m aware that there is one person who claims to have done it, but I think this fact is indeed fascinating and works well for a flat earth debate)
This is why people believe they went around a ball, when really they just went around in a big circle.