Menu inside a headerbar (Gtk4 with blueprint)

demo.blp

using Gtk 4.0;
using Adw 1;

menu menu {
  submenu {
    label: _("File");
    item {
      label: _("New");
      action: "app.new";
    }
    item {
      label: _("Save");
      action: "app.save";
    }
  }
  submenu {
    label: _("Edit");
    item {
      label: _("Preferences");
      action: "app.new";
    }
    item {
      label: _("Copy");
      action: "app.save";
    }
  }
}
Box welcome {
  orientation: vertical;
  
  [start]
  Adw.HeaderBar {
  Gtk.Button {
  icon-name: "open-menu-symbolic";
  }
  Gtk.PopoverMenuBar {
  menu-model: menu;
  }
  }
}