For context, Determinate is a startup made of the Nix guy and some of the senior community members. They explicitly support the Steam Deck (and used it as a test case to create their installer).
Not just senior community members, DetSys is the company of the creator of nix.
This installer and the relationship between DetSys and Nix has also been subject to major criticism about conflict of interest between community interests and DetSys, since everyone agrees the official Nix installer has major issues. "Determinate Nix" (as DetSys calls the nix configured with their installer) also enables features that are the de-facto way to use Nix these days, but are disabled in the default distribution because of... let's say... commitment issues.
If you want a community run alternative, try Lix. They have a version of the DetSys installer too - and they actually cut releases of nix instead of building moats around it.
There should (hopefully) be an ~official-nix version of the detsys installer in the ~near future. (That said, one slice of the reasons this has taken a while is that the upstream Nix variant is obliged to stick to official features for now.)
It's basically at the point where it just needs a redirect from the nixos.org domain, and for the project/community to work through how to manage its development/relationship to the Nix repo.
Lix is excellent. It is already faster (parsing), safer (better defaults, removed footguns), and easier to use (better errors, etc) than Nix. If anyone wants to get started using Nix then I highlight recommend you install Lix from the link in the parent comment.
Lix is a fork of Nix (the program, "CppNix") and also an alternative community. They provide a few ways to install, like nixpkgs itself, but also a DetSys installer fork.
It's generally a response to corporate interests (including Anduril, who put Nix on autonomous weapons) and elbow-shoving so-called meritocracy (including a very infamous concern troll) becoming dominant inside the Nix community and Nix leadership, by people who didn't want to work from inside the system to reform, but also know they can't maintain all of Nixpkgs by themselves either (which already bled a bunch of maintainers).
https://determinate.systems/posts/nix-on-the-steam-deck/