Installation

use the official installer image with Calamares to install NixOS as usual (feel free to add no desktop environment for a way faster build)
make sure to name the user just like your main user on that system is going to be called (to not get UID conflicts with SOPS)
reboot into the newly installed system

add the following to /etc/nixos/configuration.nix:

services.openssh.enable=true;
nix.settings.experimental-features = [ "nix-command" "flakes" ];
environment.systemPackages = with pkgs; [ git ];

sudo nixos-rebuild switch
login via ssh
copy /etc/nixos/hardware-configuration.nix to your hosts hardware-configuration.nix in your flake, add, commit, push
replace /etc/ssh/ssh_host_ed25519_key with your hosts' intended SSH key
add ~/.ssh/id_ed25519, and run chmod 600 ~/.ssh/id_ed25519
run nix develop github:charludo/nix#keyctl and use enable-user and sudo enable-host to set up the sops keys
run sudo GIT_SSH_COMMAND='ssh -i /home/<username>/.ssh/id_ed25519 -o IdentitiesOnly=yes' nixos-rebuild switch --flake github:charludo/nix#<your_host> to install the system properly this time

charludo / nix