the Warnings buffer says:

Warning (initialization): An error occurred while loading ‘/nix/store/4zw8l9f2ybgq5klckdl5dh9ygvcghq32-emacs-28.2/lib/emacs/28.2/native-lisp/28.2-78b7c535/warnings-28e75f4d-870b026e.eln’:

Doom hasn't been initialized yet; did you remember to run 'doom sync' in the shell?: /nix/store/9prmp4wm3y282kdjbmdmksmija0p38m6-straight-emacs-env/etc/@/init.28.elc

To ensure normal operation, you should investigate and remove the
cause of the error in your initialization file.  Start Emacs with
the ‘--debug-init’ option to view a complete error backtrace. Disable showing Disable logging

In reply to @alicecandyom:krendelhoff.space

here is workaround I did to fix it:

(use-package! consult
  :config
  (defun consult--ripgrep-builder (&rest args) (apply (consult--ripgrep-make-builder) args)))

Ha! Adding po-mode from MELPA was as simple as

{ config, pkgs, ... }:

let
  doom-emacs = pkgs.callPackage (builtins.fetchTarball {
    url = https://github.com/nix-community/nix-doom-emacs/archive/master.tar.gz;
  }) {
    doomPrivateDir = ./doom.d;
    emacsPackagesOverlay = self: super: {
      po-mode = pkgs.emacsPackages.po-mode;
    };
  };
in {
  home.packages = with pkgs; [
    doom-emacs
  ];
}

Ha! Adding po-mode from MELPA was as simple as

{ config, pkgs, ... }:

let
  doom-emacs = pkgs.callPackage (builtins.fetchTarball {
    url = https://github.com/nix-community/nix-doom-emacs/archive/master.tar.gz;
  }) {
    doomPrivateDir = ./doom.d;
    emacsPackagesOverlay = self: super: {
      po-mode = pkgs.emacsPackages.po-mode;
    };
  };
in {
  home.packages = with pkgs; [
    doom-emacs
  ];
}

...but alas, it doesn't work. I get Invalid function: po-with-temp-buffer when opening a .po file.