You don’t want to modify the engine cube, because you probably want it to cube shaped in the future. Also, the cube needs to be high poly, which the engine one is not. Best to make your own in modelling mode.
There’s no displacement of materials any more in 5, because of Nanite. But you can still displace meshes using the geometry tool.
The displacement map is in the red channel of that strange yellowy texture. That’s why those textures are called something like …ORDp ( Opacity, Roughness, Displacement ).
Ok, it must be something new that I missed.
By the way, how do I use the “displacement” function if it is not linked to the material?
What to connect and how?