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.
The way you updated from github isn't the right way. You can't cherry pick certain files from one commit, as each commit may have dependencies on previous commits. This can lead to subtle and nasty problems. Which is bad for you (!) and also bad for us, if your site starts exhibiting issues nobody else is seeing, because of your particular mix of files, and we don't know what's been updated and what hasn't.
Whenever you do a github update, you MUST update ALL files. Easiest way is just to grab the ZIP from:
https://github.com/Fabrik/fabrik/zipball/master
... unzip it, and copy the content of the inner, numbered, folder up to your server, making sure you overwrite all existing files. Yes, this takes a little extra time (especially now we have the DOMPDF library, which adds a lot of files), but if you use something like FileZilla, is just a few mouse clicks.
-- hugh