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.
I understand especially since this is free support. I know you guys accept projects such as this, can we offer to pay for your expedited attention to this? What would it cost?
thanks,
Jeff