I answer you by parts:
The maximum speed of an F-16 is mach 2.05, neither more nor less, and it is reached between 30,000 and 45,000ft. Depending on the temperature of the tropopause the top speed can increase or decrease. The attached graph is from ISA at 15 degrees:
But rarely does this plane in real life reach even 2.05 unless it has an almost empty tanks.
About the second thing, and I think I already answered you: all the functions of the airliners that were in the F-16 have been removed since it is not an airliner. The hud has a mach indicator and that’s what the real plane has. That there was a button on the right MFD that would allow you to switch from CAS to Mach was a feature, but not a real feature and therefore not a real priority to add it again.