Actually, the post's solution, besides being built on top of direnv, uses Devbox, which itself is built on top of Nix... https://www.jetify.com/devbox/docs/faq/#how-does-devbox-work So they are saying they are outside the Nix ecosystem when in fact they are in it. It is yet another set of nice scripts on top of Nix.
They mention Nix but I guess they are referring to the use_nix integration built-in to direnv? There is a fairly detailed (but old) comparison in https://github.com/direnv/direnv/wiki/Nix#some-factors-to-co... and in the meantime lorri and nix-direnv are the only ones still maintained. But you aren't limited to Nix when using direnv, for example there is nvm. https://github.com/direnv/direnv/wiki/Node#using-nvm
Actually, the post's solution, besides being built on top of direnv, uses Devbox, which itself is built on top of Nix... https://www.jetify.com/devbox/docs/faq/#how-does-devbox-work So they are saying they are outside the Nix ecosystem when in fact they are in it. It is yet another set of nice scripts on top of Nix.