Hmm documentation problem. Are you trying to get NixOS (the operating system) or Nix the package manager? NixOS the operating system doesn't work on Windows, but it is Linux? You know what I mean its an operating system.

Anyway the download link is here: https://nixos.org/download#nix-more

The first section "Nix: the package manager" as you can see works on Linux, Mac, Windows subsystem for Linux (WSL)

The second section "NixOS: the Linux distribution" is what you use if you want to reimage your computer. I would just use the Graphical ISO image. Even if you wanted a virtual machine on virtualbox instead of reimaging your computer, you can still just use the iso image for that.