it works :D

modules/system-settings/amd-gpu.nix

@@ -0,0 +1,5 @@
+{
+	flake.modules.nixos.amd-gpu = { pkgs, ... }: {
+		boot.kernelModules = [ "kvm-amd" ];
+	};
+}

modules/system-settings/i18n-de.nix

@@ -0,0 +1,21 @@
+{
+	flake.modules.nixos.i18n-de = {
+		time.timeZone = "Europe/Berlin";
+
+		i18n.defaultLocale = "en_US.UTF-8";
+		i18n.extraLocales = [ "ja_JP.UTF-8/UTF-8" ];
+
+		i18n.extraLocaleSettings = {
+			LC_ADDRESS = "de_DE.UTF-8";
+			LC_IDENTIFICATION = "de_DE.UTF-8";
+			LC_MEASUREMENT = "de_DE.UTF-8";
+			LC_MONETARY = "de_DE.UTF-8";
+			LC_NAME = "de_DE.UTF-8";
+			LC_NUMERIC = "de_DE.UTF-8";
+			LC_PAPER = "de_DE.UTF-8";
+			LC_TELEPHONE = "de_DE.UTF-8";
+			LC_TIME = "de_DE.UTF-8";
+		};
+		console.keyMap = "de";
+	};
+}

modules/system-settings/linux-latest.nix

@@ -0,0 +1,5 @@
+{
+	flake.modules.nixos.linux-latest = { pkgs, ... }: {
+		# boot.kernelPackages.pkgs.linuxPackages_latest;
+	};
+}

modules/system-settings/systemd-boot.nix

@@ -0,0 +1,6 @@
+{
+	flake.modules.nixos.systemd-boot = {
+		boot.loader.systemd-boot.enable = true;
+		boot.loader.efi.canTouchEfiVariables = true;
+	};
+}