The final audio fidelity is dependent on the underlying audio hardware along with the Audio framework (WASAPI). Since Windows 10/Server OS shares the same framework (WASAPI), I don't believe one will sound better than the other.
Yes : if Rest of your Chain is capable of Showing the difference between 2 Similar Software OS.
No : If your rest of the Chain is not resolving enough..
The newest iteration of Windows is Supposed to sound Sonically better, so there's a difference in the sonic performance between different Windows iterations.
Yes. Different versions of OS has different background tasks, etc and are quite likely to sound different, provided you take the effort to optimize them for audio. If you leave it stock then they are likely to be noisy enough by default that the changes may get masked.
I was using Windows 2012R2 version, recently installed 2019 Datacenter and yes this version sound better than 2012.Background is more silent and highs are more clear.