M.C.Escher's Relativity-CAM

I want to create a 10x10x10 cube sculpture inspired by M.C. Escher's Relativity.

I built the first model in Fusion directly. During the face-1 step, the tool head is not from top-down direction. And I realized that the XYZ axis was wrong. Meanwhile, I am not very satisfied with the design, so I move to Rhino for step 2.

In the second model, I made a mistake. I place stairs in the middle of the opening, which is not possible to CAM.

In the third design, my approach is using the boolean difference from outside for the desired outcome. This way, I can make sure there is no overhang element.

I save the 3D file as STL, and import it to Fusion.

The facing simulation is smooth. However, for 2D adaptive clearing, I could not select the pocket as shown in the pink model. So, I cover the mesh to brep, as shown in the black model in the next step

My problem is, I need to select every signle face in one pocket. I think it is because the model is covered from the mesh stl model. I don't know how to solve this issue yet.