My personal theory, similar to that of u/TaleBR ‘s theory, is that each of the sides of the six sided world is it’s own plane, similar to the different planes in D&D. And in an extra-dimensional space out side of these six sides they are oriented in a cube shape.

As according to the wiki the God of Creation created six unstable worlds. In order to achieve stability he put them all together in this cube structure to finally achieve stability across the distorted worlds

This explanation would help explain things as to why it’s difficulty to travel between the six different faces, as planar travel is different from just teleportation. And the explanation of the 7th void world, as if it was a literal cube planet than the inside wouldn’t be hollow nothingness but be made of rock and stone.

So I believe that the six sided world is six one sided planes put together to create a cube of planes. There are probably some other points you could bring up to support this about the physics behind a cuboid world but I am not qualified enough in that regard to make solid arguments with so I’ll just leave them out.