In this position, again no piece can move along the hyper diagonal, so the black King and the white Bishop on d5[3] don't see each other.
The Knights move the normal Knight's move in any of the orthogonal planes, e.g. Nb3[1]-a1[1], Nb3[1]-b2[3], but not Nb3[1]-a1[2]
This is a mate in 3.
3D-Position:
Apologize for not having a fancy 3D visualization. The picture shows, from left to right, layers 1, 2, 3 and 4.
In notation I'll use square brackets for the additional coordinate.
Assume that Queen and King cannot move along the hyperdiagonal, so the Queen on c4[2] is not giving check to the black King on b5[1] (and black King is also not attacking that Queen).
Then question is, is this a forced mate and in how many moves?
Spoiler
Now last few days I extended my engine to 3D and it says that this is mate in 4, first move is Qb3[2]-b4[2].