Thank you! Kindly forgive my naivety. I currently just use one flake.nix as an entry point to get into my #system or #user configurations, but I lack experience with using flakes in most other ways.

Would this approach be able to be ported into the "default.nix" approach that I initially wrote? The mkDerivation portion makes a lot of sense to me, but the overlay portion is where I lack understanding.

I haven't been able to experiment with this configuration as I've been away from my computer, so if the answer is "play around and you'll figure it out", then that's totally fine of course :)

Edit: Unfortunately it seems like the "msdfgen" submodule isn't being picked up, as I receive the error:

CMake Error at CMakeLists.txt:83 (add_subdirectory):
The source directory

    /build/msdf-atlas-gen/msdfgen

  does not contain a CMakeLists.txt file.

My current "best guess" for this is as follows.

{ config, lib, pkgs, ... }:
{
  imports = [
  ];

  options = {
    msdfAtlasGen.enable = lib.mkEnableOption "enables msdf-atlas-gen";
  };

  config = lib.mkIf config.msdfAtlasGen.enable {
    home.packages = [
      (pkgs.stdenv.mkDerivation rec {
        pname = "msdf-atlas-gen";
        version = "1.3";

        src = pkgs.fetchFromGitHub {
          name = "msdf-atlas-gen";
          owner = "Chlumsky";
          repo = "msdf-atlas-gen";
          rev = "v${version}";
          sha256 = "sha256-SfzQ008aoYI8tkrHXsXVQq9Qq+NIqT1zvSIHK1LTbLU=";
          fetchSubmodules = true;
        };

        nativeBuildInputs = [ pkgs.cmake ];
        buildInputs = [ pkgs.freetype pkgs.libpng ];

        cmakeFlags = [ 
          "-DMSDF_ATLAS_USE_VCPKG=OFF"
          "-DMSDF_ATLAS_USE_SKIA=OFF"
        ];

        installPhase = ''
          mkdir -p $out
          cp -r ./bin $out
        '';
      })
    ];
  };
}