KDE Connect

KDE

programs.kdeconnect.enable = true;

KDE via Home Manager

home-manager.users.username.services.kdeconnect.enable = true;

networking.firewall = rec {
  allowedTCPPortRanges = [ { from = 1714; to = 1764; } ];
  allowedUDPPortRanges = allowedTCPPortRanges;
};

GSConnect (for GNOME)

programs.kdeconnect = {
  enable = true;
  package = pkgs.gnomeExtensions.gsconnect;
};

Then enable "GSConnect" extension.

GSConnect via Home Manager

home-manager.users.username.programs.gnome-shell = {
  enable = true;
  extensions = [{ package = pkgs.gnomeExtensions.gsconnect; }];
};

networking.firewall = rec {
  allowedTCPPortRanges = [ { from = 1714; to = 1764; } ];
  allowedUDPPortRanges = allowedTCPPortRanges;
};

This will auto-enable extension for you.