This command adds inputs to the lock file of a flake (flake.lock) so
that it contains a lock for every flake input specified in flake.nix.
Existing lock file entries are not updated.

If you want to update existing lock entries, use nix flake update

nix flake update does update other referenced flakes, but not nixpkgs. my flake is a longer business, here's the inputs section:

inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.05";
    nixpkgs-unstable.url = "github:NixOS/nixpkgs/nixos-unstable";
    utils.url = "github:numtide/flake-utils";
    home-manager = {
      url = "github:nix-community/home-manager/release-24.05";
    };
    colmena = {
      url = "github:zhaofengli/colmena/v0.3.2";
      inputs.utils.follows = "utils";
    };
    dsa41heldendokument = {
      url = "github:flyx/DSA-4.1-Heldendokument";
      inputs.nixpkgs.follows = "nixpkgs";
      inputs.utils.follows = "utils";
    };
    nimyaml = {
      url = "github:flyx/NimYAML";
      inputs.utils.follows = "utils";
    };
    nyarna-web = { url = "github:nyarnalang/website"; };
  };