I'm assuming you come from the default NixOS GNOME install.

1. Clone this repository.
2. Copy your /etc/nixos/hardware-configuration.nix to the <repo>/src/hardware-configuration.nix
3. In the <repo>/flake.nix make sure you change the username to the one you used when you installed NixOS.
4. Rebuild the system with sudo nixos-rebuild switch --flake '.#fred'. Just replace fred with your username.
5. TO BE CONTINUED...

If keystore keeps asking for a password, it means it could not be unlocked automatically, we can delete the keyring file to fix this. Next time, when asked for a password, leave the password EMPTY - so that the Display Manager can unlock it on auto-login.

Delete the login.keyring file:

rm .local/share/keyrings/login.keyring