code: public function set_submenu() {
  
  		$submenu = Module::CustomRatingGrifus()->getOption( 'submenu' );
  
  		WP_Menu::add(
  			'submenu',
  			$submenu['custom-rating-grifus'],
  			[ $this, 'render' ],
  			[ $this, 'add_scripts' ],
  			[ $this, 'add_styles' ]
  		);
  	}
docs: Add submenu for this page.
  
  @uses add_submenu_page() → add a submenu page