If you want graphical apps to be handled by nix on macos, you might be interested in <https://github.com/BatteredBunny/brew-nix>. nixpkgs does not package macos sandboxed apps AFAIK, that means typically only cli utilities, libraries and development tools only work.
Tried this when it was released on HN. It does not work out of the box. There is some problem with launching apps from outside of the applications folder. The trampoline Mac-app-útil approach does not work. Though in theory it probably should for most applications. I don’t know enough about the code signing process to be able to debug what is wrong with it.
