This repo is inspired by https://gitlab.inria.fr/nix-tutorial/packages-repository and contains software that I haven't figured out how to properly package yet. It's whatever, but kinda works...
change your configuration.nix to something like this:
{ config, pkgs, ... }:
let
tttttx2 = import (fetchTarball https://github.com/tttttx2/NixOS-Packages/archive/main.tar.gz) {};
in
{
environment.systemPackages = [
tttttx2.mito
];
}
add this repo as a channel
nix-channel --add https://github.com/tttttx2/NixOS-Packages/archive/main.tar.gz tttttx2
nix-build -E 'with import <nixpkgs> {}; callPackage ./XXX.nix {}'
nix-shell --pure -E 'with import <nixpkgs> {}; callPackage ./XXX.nix {}'