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
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I noticed this problem over a week ago but never posted. When I saw this thread I thought it would be fixed for me after a github update. But I just updated from github and the problem still remains.I think I may have just fixed this in github.
-- hugh
Is it ok e.g. in the backend or with a menu item?The only caveat I can think of is that this Yes/No element is in a Fabrik module form.