Windows had one for DOS, Windows 16, "posix" and "os/2" with the last two in air quotes because it was only a subsection and they claimed mission accomplished - I think it was specifically to satisfy some government requirement but don't use me as a reference here. I don't think it could do os/2 "Presentation Manager" for instance. And there was a reason that cygwin was still a thing. I used it for an actual production project maybe 22 years ago. Wow, you've never seen slow until you run cygwin bash scripts on windows 2000.
Regardless, it didn't come free - there's people up in Redmond who had that as part (or maybe all) of their job. I would have done that - maintain an esoteric part of Windows for a Microsoft salary? That's the kind of job where you have almost no boss. Sign me up.
They had a bunch of weird projects like that. IE for Unix which ran on Solaris and HPUX (evolt has them: https://browsers.evolt.org/browsers/archive/ie you can probably QEMU that if you want). They also had Alpha, MIPS and I believe PPC versions of windows. There were a lot of other things that never got done. Like Windows for Intergraph Clipper, a fact that someone somewhere has decided to vouch for me on 12 years ago over yonder: https://www.cpushack.com/2011/01/16/cpu-of-the-week-intergra...
Again, all this shit I know? totally useless.