Talk: Unfree Software
From NixOS Wiki
Usage of nixpkgs.config all over the page seems misleading in light of nixpkgs PR 257458 - fail when nixpkgs.config is set with explicit pkgs, remove all nixpkgs.config usages in in-tree modules.
There is no native support for defining unfree software in multiple places - nixpkgs issues 197325. There is a solution in the comments of this issue. It might be worth including in the page until native support is provided.