In reply to @wantguns:matrix.org
if there is an example flake i can follow which uses the output / config of a darwinConfiguration as colmena's host's options, that would help a lot

In your flake.nix on line 43 you have

nixpkgs = import nixpkgs { system = "x86_64-linux"; };

I'm suggesting you instead write

nixpkgs = import nixpkgs;

# ...
      deploy = {
        nodes = builtins.mapAttrs (name: hostConfig:
          let 
            isDarwin = hostConfig.platform == "darwin";
            activationPath = if isDarwin 
              then deploy-rs.lib.${hostConfig.system}.activate.darwin self.darwinConfigurations.${name}
              else deploy-rs.lib.${hostConfig.system}.activate.nixos self.nixosConfigurations.${name};
          in {
            hostname = hostConfig.hostname;
            profiles.system = {
              user = if isDarwin then hostConfig.username else "root";
              path = activationPath;
            };
          }
        ) hosts;
      };
# ...