Does the popup happen at the same spot or does it happen anytime in the workflow?
I would open “UiExplorer” and see what selectors are available.
This will depend on when the popup appears but I would try a ‘Pick Branch’ to check for the popup with an ‘Element Exists’ (just need to find the selector for the ‘Ok’ button or the ‘window’).
Try to use strict selector on the button that will trigger the java pop-up, and change the click type from simulate click to hardware events, then use hotkey trigger “enter”. Do not use Fuzzy Selector.