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
See Announcement
We have resolved the issue with the J! updater and this will be fixed in the next release.
So ... how far did you get with github? Did you get as far as installing git locally, creating your SSH keys, and adding the public key to your github account?
-- hugh
Pull request approved, many thanks.
-- hugh