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.
what error message did you get?joomla seach was getting crashed.
Have you installed enabled Fabrik search?
What release of Fabrik are you on? Are you using a github release?