themes-wordpress/lineup/patterns/404.php

<?php
/**
 * Title: A 404 page
 * Slug: lineup/404
 * Inserter: no
 */
?>
<!-- wp:heading {"level":1,"anchor":"nothing-found"} -->
<h1 class="wp-block-heading" id="nothing-found"><?php echo esc_html__( 'Nothing found. Search?', 'lineup' ); ?></h1>
<!-- /wp:heading -->