Since version 2.0.1 of ArcGIS Pro, I was able o do something which was probably not documented but was really usefull especially to those who don't have a 3d analyst license.
Extruding a polygon, and then copying and pasting (special) it into an empty multipatch featureclass would preserve the extrusion, thus leading to a perferctly nice-looking-complete multipatch!
This is not possible with the last version (2.1) anymore. The exact same procedure (tested) produces multipatch which are only more or less one meter tall (thick) no matter of the look the extruded polygons had.
Maybe this hidden functionality was not even meant to be, but since I found it out, would it be possible to know if this is a bug?