I think this was posted above but to clarify:
Either use the OSNAPZ variable (more info in help) or in Options on the Drafting tab check the box near "Replace Z value with current elevation". They both do the same thing.
Jeff Paulsen
Civil 3D 2020.4 | Win 10 Pro N 64-bit
Xeon W-2223 @ 3.60GHz, 32GB Ram | NVidia Quadro P2200