All 3 axes are fourfold and can thus all equivalently be chosen as the z-axis for the PAS. Since it’s all neat, the EFG tensor vanishes.
We have a fourfold rotation for Fe-IIa int he xy-plant (taking the arrow in the picture as z) and a 2 fold rotation on the other planes. We can thus choose this fourfold rotation axis as the PAS for a system with an eta of 0. But the EFG tensor will not vanish as in the previous example.