I am running a Linux laptop, and I regularly run and test code on Windows, macOS, FreeBSD, OpenBSD, NetBSD, DragonFly BSD, and illumos. Basically, all the systems Go supports minus Solaris and AIX because they're proprietary and I can't "just download" them AFAIK, and Plan 9 because I found it too confusing/hard to set up (and is so obscure I don't really care too much either).

The "Pixie dust" is QEMU and a zsh script.

GitLab doesn't outright ban Windows for any and all usages; you just can't run it on your laptop as the main system (although exceptions are allowed).

And naturally you can answer any Windows support question as good as a Windows developer that is running their system 8h a day.

I surely won't regarding UNIX flavours, and have been using them in some variation since 1992.

Virtual machines aren't that magic I'd say, but sure, if you think they are pixie dust, then I guess its pixie dust...

No Windows allowed....

again, "on company laptops". Surely the concept of remotely accessing VMs is not new to you?

As it is the lack of skills for a given OS people don't use on their systems.