[Smaug123]

Maybe you got confused (like I did every time until I stopped doing anything non-flakey) about when `nixpkgs` is called `nixpkgs` and when it's called `pkgs`? In the flakes world it's considerably easier because everything is explicitly named, so you take an actual decision about what to call it.

[baby]

Is the convention to call it pkgs when you instantiate it with a system?

[cmm]

yes. other possible arguments are overlays and package selection modifiers (like whether to include non-free stuff or stuff that is marked as broken).