Custom material expression and scene texture

Hello, I know it’s a bit late but it can be useful for other people,

the pin World Position Offset accept only one Vector3 because it moves the whole object from this Vector3.

I think that the pin you want to use is World Displacement, you have to enable Tessalation (click on the material Node and in panel details, search Tesselation and change No Tesselation to Flat Tesselation).