Edit /includes/modules/pages/sitemapxml/sitemapxml_manufacturers.php, line 41 ... adding the highlighted bit
Code:
        $sitemapXML->writeItem(FILENAME_DEFAULT, 'manufacturers_id=' . $next_manufacturer['manufacturers_id'], $next_manufacturer['languages_id'], $next_manufacturer['last_date'] ?? $last_date, SITEMAPXML_MANUFACTURERS_CHANGEFREQ, $xtra);
Thanks for the report!