The Wilderlands of High Fantasy
The Cosmology of the Wilderlands was developed before the 1st Edition Player’s Handbook, so it wasn’t designed with that planar cosmology in mind. The people of the Wilderlands have their own cosmology.
The Prime Material is the universe in which the planet of the wilderlands exists. It’s our universe, someplace in the Milky Way Galaxy. Space travel is a real possibility, even space travel to Earth and other planets. The planet of the Wilderlands does not exist in a place of Wildspace, however. Real World Physics is involved, so transport has to happen by some other magical means (a starcaster drive?) or technological (hyperspace drive, warp, Time Dilation, Generation Ships for example). Sages often claim that the Prime and the universes in it represents the ultimate embodiment of Law.
The Void is truly Chaos, Element. It surrounds the Universe and it is infinite in scope.
The Absolute World
Nothing is known about the Absolute World except it is the place where Perfect Truth, Light, and Beauty resides. Some Sages believe that the Absolute World is the Source of all that is, the True Source of Absolute Truth. Sages who disagree with the Sages mentioned above believe that the Absolute World is the absolute embodiment of Good and Law.
There are other versions of the Wilderlands. Some ahead in time, some behind in time, some diverging as a result of different events. There are an infinite number of these Alternate Primes, as infinite as the beings that inhabit them.