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.
foreach ($this->headings as $key => $heading)
$this->headings = array_replace(
array_flip(
array('table_name___el_name1','table_name___el_name2','table_name___el_name3')
), $this->headings);
foreach ($d->filters as $key => $filter)