Well, some people claim that non-Server Windows can't ever be used in a server role, even with third-party software, and that you need a CAL for every person connecting to third-party software on Windows Server, so it's at least possible.
> Except as otherwise permitted by
the terms of this License or otherwise licensed by Apple: (i) only one user may use the Apple Software at
a time, and (ii) you may not make the Apple Software available over a network where it could be run or
used by multiple computers at the same time
It's of course debatable whether, say, using the built-in file sharing counts as "making the Apple Software available", doubly so for third-party servers, but that's exactly the argument some of those Microsoft licencing people are making.
This sounds like they're trying to prevent people running farms of Mac minis AWS style, rather than using them as a server. But a highly paid Apple layer may still disagree.
And, indeed, Apple does have a similar clause in their EULA: https://www.apple.com/legal/sla/docs/macOSMonterey.pdf
> Except as otherwise permitted by the terms of this License or otherwise licensed by Apple: (i) only one user may use the Apple Software at a time, and (ii) you may not make the Apple Software available over a network where it could be run or used by multiple computers at the same time
It's of course debatable whether, say, using the built-in file sharing counts as "making the Apple Software available", doubly so for third-party servers, but that's exactly the argument some of those Microsoft licencing people are making.