I am attempting to extrude down along the Z axis the four vertices I have selected on the right side of the NURBS surface in this file:
This thread shows how to do the extrusion I am attempting:
I find I am unable to do so. When I attempt to extrude using the shortcut key sequence E Z, there is no extrusion. Instead it acts the same as the sequence G Z, and moves the vertices instead of extruding them. What is going wrong here?
My Blender version is 2.90.1