How to set the keyboard layout in plasma_wayland

I am trying to use plasma_wayland without X11, i.e.

console.keyMap = "sg";

services.xserver = {
  enable = false;
  layout = "ch";
}

services.greetd = {
  enable = true;
  settings = {
    default_session.command = ''
      ${pkgs.greetd.tuigreet}/bin/tuigreet \
        --time \
        --asterisks \
        --user-menu \
        --cmd startplasma-wayland
    '';
  };
};

On the login screen I still have the SwissGerman keyboard sg.
but Plasma or Waylanmd switches to us layout.

How can I tell them to use sg layout too?

Thanks for your help.