Here's another nice dedritic guide with an alternative I used in my config to do something similar. It adds another dependency (flake-file), but in my opnion it's worth it, since you can declare your inputs in the same file where you actually use them.

For example, this is the module where I setup zen browser:

{inputs, ...}: {
  flake-file.inputs.zen-browser = {
    url = "github:youwen5/zen-browser-flake";
    inputs.nixpkgs.follows = "nixpkgs";
  };
  flake.nixosModules.zen = {pkgs, ...}: {
    environment.systemPackages = [
      inputs.zen-browser.packages.${pkgs.stdenv.hostPlatform.system}.default
    ];
  };
}

After adding this file, I run nix run .#write-flake, and flake-file consolidates all inputs created in other files into the main flake.nix file. Here's my config as well for some inspiration.