By default for being earthlike, the yugioh dimension starts as a 4d space time. There are three spatial dimensions of length, width and height with the additional non-spatial dimension of time. There is a statement that there is a "space between spaces.", this clear states that the dimension has an additional spatial dimension. Now, we discussed the earlier radar image and I brought up that a map can display a projection of a space of higher dimension, however there is another way to interpret it: that could also be a map of the space between spaces, and since it is clearly a 2d map, that would mean that there is at least additional spatial dimensions, though this isn't confirmed.
So the yugioh GX cosmology is at least a 5d space time, possibly a 6d space time. It could also be higher, though I don't have any evidence to support it.