See attached Screenshots. In Form View there is no form "TopKontor Zeiterfassung Download " but in Group View I can see the form in the Filter DropDown.
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.
Puh, no idea if this is or ever has been working correctly.