As of recently, Nix 2.6 from Ubuntu 22.04 became too old to evaluate
nixpkgs. A new-enough version of Nix is available as part of Ubuntu
24.04, but those newer versions of Nix aren't happy with our rather
primitive proot workaround anymore.
Thankfully, someone already made a version of Nix that does all the
heavy lifting for running in unprivileged environments like the one
Read the Docs provides. So we used that instead.
Martin Weinelt
emilylange
Naïm Favier
Antoine Eiche