https://github.com/formthefog/lasr/blob/main/flake.nix#L217
This is a project I was working on to create a generic debug VM to run a node for my team to test. It works on MacOS, opens up a Linux qemu instance.
Incredible success story: I got nodejs to build as linux -> freebsd cross by injecting some intermediate binaries from the native linux build. https://github.com/NixOS/nixpkgs/pull/384413
Is there a non-zero chance of being able to build a python app using pkgsCross.mingwW64? I'm running into issues early on with bash complaining it can't run as a pe executable (seems totally reasonable, but I'm not sure where it's decided it needs to do that)
Or alternatively, any chance of being able to build python things for windows in some form of VM/wine/something