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.
If you wish to set a label from a data value that is not an available placeholder, you can use MySQL Concat to retrieve the value by embedding a subquery within the CONTACT Label field:
Code (Text):
(SELECT `column_containing_desired_value` FROM other_table WHERE `id` = {thistable}.field_containing_foreign_key)