nextcloud-server/apps/updatenotification/templates/admin.php

<?php
declare(strict_types=1);
/**
 * SPDX-FileCopyrightText: 2018 Nextcloud GmbH and Nextcloud contributors
 * SPDX-License-Identifier: AGPL-3.0-or-later
 */
\OCP\Util::addScript('updatenotification', 'updatenotification');
?>

<div id="updatenotification"></div>