nix-flake/modules/components/boot-loaders/grub.nix

{ inputs, self, ... }: {
  flake.nixosModules.global = { pkgs, config, lib, ... }: {
    boot.loader.grub = lib.mkIf (config.components.bootLoader == "grub") {
      enable = true;
      useOSProber = true;
    };
  };
}