idk if 2 users is fair, it may just be my circles but I see nixos mentioned more than almost anything else on lemmy/hn/etc in the past couple years

the instructions for installing on not nixos https://nixos.org/download/

plenty of package managers have.

flatpak doesn’t require any admin to install a new app

nixos doesn’t run any code at all on your machine for just adding a package assuming it’s already been cached. if it hasn’t been cached it’s run in a sandbox. the cases other package managers use post install configuration scripts for are a different mechanism which possibly has root access depending on what it is.

alpine fits that, or derivatives like postmarketos

have you considered https://github.com/a-schaefers/systemE plus https://github.com/emacs-exwm/exwm ? that’s basically an entire emacs userland