Is it impossible to extrude a subd model?

Is it impossible to extrude a subd model?


I want to make the thickness of the visible model 3mm.

Is there any way?

You can use Joint Push Pull to do that: https://sketchucation.com/pluginstore?pln=JointPushPull

From the two questions you have posted it appears you are trying to learn an advanced tool without knowing the basics.
I’d suggest to do a bit of basic learning first.