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.
This looks ok, "Render as Dropdown" will display the dropdown caret and open the dropdown with the buttons on click (same as in F3).
Doesn't it open on click in your case? Is it ok with Cassiopeia (or Atum in the backend)?
Obviously you didn't scroll down to the end of your frame.
BTW: Where is this vertical scrolling coming from.
overflow-x:auto;