themes-wordpress/indice/patterns/404.php

<?php
/**
 * Title: A 404 page
 * Slug: indice/404
 * Inserter: no
 */

declare( strict_types = 1 );
?>

<!-- wp:paragraph -->
<p><?php echo esc_html__( 'Ooops, page not found.', 'indice' ); ?></p>
<!-- /wp:paragraph -->