add boot splash screen

system/boot.nix

@@ -0,0 +1,42 @@
+{ config, pkgs, inputs, ... }: {
+  console = {
+    font = "ter-132n";
+    packages = [pkgs.terminus_font];
+    earlySetup = false;
+  };
+
+  boot = {
+    consoleLogLevel = 0;
+    initrd.verbose = false;
+    kernelParams = [
+      "quiet"
+      "splash"
+      "boot.shell_on_fail"
+      "loglevel=3"
+      "rd.systemd.show_status=false"
+      "rd.udev.log_level=3"
+      "udev.log_priority=3"
+    ];
+
+    initrd.systemd.enable = true;
+    loader = {
+      # It's still possible to open the bootloader list by pressing any key
+      # It will just not appear on screen unless a key is pressed
+      timeout = 0;
+      efi.canTouchEfiVariables = true;
+      efi.efiSysMountPoint = "/boot/efi";
+      systemd-boot = {
+        enable = true;
+        # editor = false;
+        # configurationLimit = 100;
+      };
+    };
+    plymouth = {
+      enable = true;
+      theme = "red_loader";
+      themePackages = [
+        pkgs.plymouth-theme-red
+      ];
+    };
+  };
+}

system/configuration.nix

@@ -2,14 +2,9 @@
 # your system.  Help is available in the configuration.nix(5) man page
 # and in the NixOS manual (accessible by running ‘nixos-help’).
 { config, pkgs, inputs, ... }: {
-  imports = [ ./gamemode.nix ./cachix.nix ./media-packages.nix ];
+  imports = [ ./gamemode.nix ./cachix.nix ./media-packages.nix ./boot.nix ];
   packages.media-packages.enable = true;
 
-  # Bootloader.
-  boot.loader.systemd-boot.enable = true;
-  boot.loader.efi.canTouchEfiVariables = true;
-  boot.loader.efi.efiSysMountPoint = "/boot/efi";
-
   boot.kernelPackages = pkgs.linuxPackages_latest;
 
   boot.kernel.sysctl = {