home-manager/docs/manual/usage/graphical.md

Graphical services

Home Manager includes a number of services intended to run in a graphical session, for example xscreensaver and dunst. Unfortunately, such services will not be started automatically unless you let Home Manager start your X session. That is, you have something like

{
  # …

  services.xserver.enable = true;

  # …
}

in your system configuration and

{
  # …

  xsession.enable = true;
  xsession.windowManager.command = "…";

  # …
}

in your Home Manager configuration.