Nix (on Mac / Darwin) freezes / gets stuck during Installation of Flake

I use Nix on Mac OS / Darwin. When attempting to install a custom flake (representing a custom Emacs package), it gets stuck during the installPhase of emacs-seq. This happens each and every time I try it. Rebooting does not help.

Any idea how to prevent Nix from getting stuck? Or how to debug this?

This is the command: nix --extra-experimental-features "nix-command flakes" profile install --impure ~/store/host/permanent/flakes/emacs-29/

Here is the flake.nix:

{
  inputs.emacs-overlay.url = "github:Nix-Community/emacs-overlay/master";
  inputs.emacs29-src.url = "github:emacs-mirror/emacs/emacs-29";
  inputs.emacs29-src.flake = false;

  outputs = { self, emacs-overlay, emacs29-src, nixpkgs }:
    let
      pkgs = import nixpkgs {
        system = "x86_64-darwin";
        overlays = [
          emacs-overlay.overlays.default
          (final : prev: {
            emacs29 = prev.emacsGit.overrideAttrs (old : {
              name = "emacs29";
              src = emacs29-src;
              version = emacs29-src.shortRev;
              withImageMagick = true;
              withToolkitScrollBars = false;
              withWebP = true;
              withXwidgets = true;
            });
          })
        ];
      };
    in
      rec {
        defaultPackage.x86_64-darwin = pkgs.emacsWithPackagesFromUsePackage {
          config = /Users/mekeor/.emacs.d/configuration.org;
          defaultInitFile = false;
          package = pkgs.emacs29;
          alwaysEnsure = true;
          alwaysTangle = true;
        };
      };
}

If you’re using Terminal.app, you should at least be able to right click, select inspector, and see what command is running.