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
Prefilter query - Optional - this can contain an SQL query that is run to get a record from the database. Its data is stored in an object that can be accessible in the pre-filters value field with the variable name $q