nix/services/sddm.nix

{ pkgs, ... }:
{
  services.displayManager = {
    defaultSession = "none+i3";
    sddm = {
      enable = true;
      theme = "sddm-i3-theme";
      settings = {
        General = {
          InputMethod = "";
        };
      };
    };
  };

  environment.systemPackages = [
    pkgs.sddm-i3-theme
    pkgs.libsForQt5.sddm
  ];
}