NixOS has a desktop installer now. If they had an easy way to setup Flathub and turn on auto updates, it would be as user-friendly as Silverblue. I actually have several family members on it, since I can do that first post-install setup.
Basically, nixpkgs is still the best way to run something on NixOS
Flatpak is an ugly hack that mixes together the completely unrelated tasks of packaging and sandboxing, while not being particularly good at any.