I had to start using nedit under Ubuntu 18.04.5 in VirtualBox under Win 10 and unfortunately encountered an intermittent problem with the keyboard input stopping to work (see post here: https://www.okob.net/wp/index.php/2021/07/30/building-nedit-ng-for-ubuntu-1804/).
After trying to use nedit-ng for a bit I decided to switch back and try to solve that keyboard input problem.
The repo with the fix is here: https://github.com/dob71/nedit
It solved the problem with the input into the edit windows, but introduced (or maybe they are unrelated) the problem with the dialog boxes.
I haven’t spent much time on the dialog boxes input problem yet. So far my solution was to link nedit statically under Ubuntu 16.04 (see “static-ubuntu16″ build configuration) where it worked flawlessly and run that executables under 18.04. It appears to work, but it has been only a week or so, not enough time to confirm for sure that the dialog boxes problem is gone. The edit windows keyboard input problem though is certainly resolved now.