MSFS, like FSX/P3D, does simulate free turbine turboprops.
(If you start any turboprop in MSFS engine RPM increases long before prop RPM does)
The problems in FSX/P3D used to be (and probably are in MSFS as well) fixed turbine turboprops.
I don’t understand the buttonmapping request for prop speed?
You are adjusting prop speed with the condition/RPM levers and (except in beta range) you can’t directly control prop pitch.
If you want buttons to select a specific prop RPM, that’s an easy one for FDM/gauge developers.