This is definitely a hack

flake.nix

@@ -16,12 +16,15 @@
     home-manager,
     i3utils,
     ...
-  } @ inputs: let
+  }: let
     system = "x86_64-linux";
 
-    pkgs = import nixpkgs {
+    pkgs =
+      (import nixpkgs {
         inherit system;
-    };
+        config.allowUnfree = true;
+      })
+      // {i3utils = i3utils.packages.${system}.default;};
 
     lib = nixpkgs.lib;
 
@@ -31,6 +34,7 @@
     }:
       lib.nixosSystem {
         inherit system;
+        inherit pkgs;
 
         modules = [
           ./hosts/${hostname}/configuration.nix
@@ -47,8 +51,6 @@
             };
           }
         ];
-
-        specialArgs = {inherit inputs;};
       };
   in {
     nixosConfigurations = {

hosts/common/default.nix

@@ -9,8 +9,6 @@
   boot.loader.systemd-boot.enable = lib.mkDefault true;
   boot.loader.efi.canTouchEfiVariables = lib.mkDefault true;
 
-  nixpkgs.config.allowUnfree = true;
-
   # nix flakes compatibility
   nix = {
     extraOptions = ''

hosts/common/graphical/default.nix

@@ -42,7 +42,7 @@
         extraPackages = with pkgs; [
           flameshot
           i3lock
-          inputs.i3utils
+          i3utils
         ];
       };
     };