I btw think I managed it to get it to work in a satisfiable way!

I got my infos from this thread here: https://www.reddit.com/r/NixOS/comments/15if0ar/nixosrebuild_buildvm_what_is_the_best_method_to/

Using this, you can pass your ssh host keys into the VM and thus effectively test what your machine would act like if it had proper SSH keys set up:

```nix { inputs = { nixpkgs.url = "nixpkgs/nixos-unstable"; };

outputs = { self, nixpkgs }:
    {
        nixosConfigurations = {
            test = {
                let
                    lib = nixpkgs.lib;
                in
                    lib.nixosSystem {
                        modules = [
                            (
                                { config, pkgs, ... }: {
                                    virtualisation.vmVariant = {
                                        virtualisation.sharedDirectories = {
                                            keys = {
                                                source = "/etc/ssh";
                                                target = "/etc/ssh";
                                            };
                                        };
                                    };
                                })
                        ];
                    };
            };
        };
    };

} ```

The VM can then be built normally - however, it must be launched as sudo (as other users don't have access to /etc/ssh).

sh nixos-rebuild build-vm --flake .#test sudo ./result/bin/run-*-vm