Standard games use flat maps.
This is a rational choice, as there is no need to create invisible parts of a game, or places that you can’t go to.
However, on a flat map, no matter how far you go you can never reach space.
If you want to create a realistic world, please refer to this tutorial.
https://dev.epicgames.com/community/learning/tutorials/qX2V/unreal-engine-connecting-earth-and-space