Do not use this without reading through the install script and understanding what it does.
This is based on Steve Strong's script at https://github.com/srstrong/nix-env, which in turn is based on our experiences at id3as and conversations on the nix forum at https://www.google.com/search?q=nix+catalina&oq=nix+catalina&aqs=chrome..69i57j0l2j69i60j69i61.5439j0j7&sourceid=chrome&ie=UTF-8.