Finding a way to install a specific version - not git commit or git tag, version - of a package is the problem.

https://github.com/NixOS/nixpkgs/issues/93327

Nix before flakes used channels, each with a flat global namespace. Flakes are intended to sit inside the git repo, so that's even less discoverable.

Nix solves practically every technical problem, but has terrible UX and documentation.