Fresh Install

nixos-generate-config --root /mnt

cd /mnt/home

git clone .../dotfiles
git clone .../nixos-config

cp /mnt/etc/nixos/hardware-configuration.nix ./nixos-config/hosts/hardware-configuration.nix

nixos-install --flake ./nixos-config#nixos

Update system, inside ~/nixos-config

nix flake update; sudo nixos-rebuild boot --flake .

also

sudo nixos-rebuild switch --flake .