It’s a result of a wpdb query.
<div class="archive-lists">
<?php $autor = $wpdb->get_results("SELECT meta_value AS autor FROM wp_posts LEFT JOIN wp_postmeta ON wp_posts.ID = wp_postmeta.post_id WHERE post_status = 'publish' AND meta_key = 'autor' GROUP BY meta_value ORDER BY meta_value") ?>
<ol>
<?php foreach( $autor as $autori ) : ?>
<div class="autor">
<li><a href="<?php echo esc_url( home_url( '/' ) ); ?>?s=<?php echo $autori->autor ?>"><?php echo $autori->autor ?></a></li>
</div>
<?php endforeach ?>
</ol>
</div>
