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.
Can you fill out http://fabrikar.com/you/my-sites with a backend login (I don't need ftp or mysql)
I send all the info, I found the prob is when I assign a confirm plugin to a form composed by multi join tables, the upload file doesn't do its job-- hugh