For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
Please see our announcement here.
$mydb = JFactory::getDBO();
$mydb->setQuery("SELECT a.params FROM #__fabrik_elements AS a LEFT JOIN #__fabrik_formgroup AS b on a.group_id=b.group_id WHERE b.form_id = '123' AND a.name = 'element_name' ");
$myparams = $mydb->loadResult();
$myobj = json_decode($myparams);
return $myobj->{'ul_directory'};