How to Hide the "Classic Editor" Admin Menu

function plt_hide_classic_editor_and_classic_widgets_menus() {
	//Hide the "Settings → Classic Editor" menu.
	remove_submenu_page('options-general.php', 'classic-editor-and-classic-widgets');
}

add_action('admin_menu', 'plt_hide_classic_editor_and_classic_widgets_menus', 11);

Where do I put this code?