Going back to the original question...
You CANNOT activate a VM using the same key as the physical because a VM uses different hardware. It uses virtualized hardware which is seen as a different machine and thus will not activate using the same key.
HOWEVER, you CAN install one or more additional instances of Windows to a VHD and natively boot those instances of Windows from the VHD. That type of installation CAN be activated using the same key because it uses the same physical hardware (it is not virtualized).
Additional clarity:
You can install Windows to Hyper-V vms and they will be unactivated and you cannot personalise it.
However, you can then native boot the vhdx file as
@hsehestedt says, and it will become activated and you can personalise it.
Thing is the personalisation gets remembered, so when you run the vm again, although unactivated, everything is personalised. Everything else works fine.
Of course, it does violate terms of EULA to run unactivated. In the old days, you could install an OS for 30 days unactivated.
But hey MS relaxed the rules from the old days where an installation went into reduced function mode. There is no time limit.
So MS dispensed with trial versions and allow you to run unactivated for an unlimited period, but then more or less contradict themselves in EULA saying you cannot run unactivated. MS even removed the watermark!
Some zealous purists will say "
just because you can run it unactivated, does not mean that you should".
My counter argument is MS could easily stop unactivated versions running (or severely restrict it). They do this with MS 365!
Frankly, it seems MS does not give a poop about Windows being activated or not. They make revenue from ads etc.!
To me, buying a cheap key (most are hidden piracy really) to activate a vm is worse than not bothering as people are being scammed, parting with cash they do not really need to. People are deluding themselves the scammers are doing them a favour just to "tick a box".
Of course, you do need an activated version of host OS or you cannot personalise it.
For avoidance of doubt, I neither discourage or encourage people to run unactivated.
As an aside, the biggest MS contradiction is using sandbox, as it is effectively runs as an unactivated "virtual machine" i.e.
you officially violate the EULA if you use sandbox (worse, it is based on Enterprise for which you need a volume licence key).
