Why the gravity and collisions don't work well when have high altitude?

Hello everyone,

In our game, the player is above the clouds, in hight altitude.

If I put a basic floor, and a basic cube above the floor with gravity and physics enable, the cube fall on the floor.

If I do the same things at 11 000 000 unit on the Z axis, the cube fall on the floor and shake.

If I do the same things at 21 000 000 unit on the Z axis, the cube fall very slowly on the floor and do very strange things, if a push it, it move like no gravity.

First, is this normal? I guess not for the strange vibration of the cube when it is in contact with the ground. But does gravity take altitude into account, like on earth?

Second, how can I fix this problem? I imagine that people wanting to create games in 1: 1 scale have already faced this problem … but I couldn’t find anything on the internet

Thanks for reading me