You can put OS X in a Windows or Linux hosted hypervisor, but the Apple doesn't want you to know about it.

You can, but it's illegal. You're only allowed to virtualise MacOS on MacOS host. You also have to obtain the system which as far as I can tell you can't buy anymore - you can only upgrade to.

Just because something is unauthorized or breaks EULA (mostly void here in EU anyway) doesn't mean it's illegal.

Even if you don't expect EULA to be enforced (will you pay for my lawyers/fine if it is?), you still need a copy of the system which you can't buy directly. You're left with unauthorised copies if you don't have any MacOS hardware and the same question - would you cover my legal costs?

You can download MacOS directly from Apple for free.

How do you legally download Big Sur without having an existing Mac machine? I thought that option was gone for some time now. A quick search doesn't bring up good solutions.

On the flip side, why would it be legal? It's looks like a pretty cut case of copyright infringement. It's their software, you're not authorized to use it, but you're using it anyways.

First it's illegal but secondly the performance is atrocious anyways (at least last time I've tried) so it won't even help you that much.

Hackintoshes break the TOS last time I checked.

Some stuff can be built for Macs from Linux, stuff like the Godot game engine supports this.

It is however a guess if they're going to allow that build or not.

Godot doesn’t build Mac binaries on Linux, the export templates provided include the platform native binaries.