I'm not sure how new this is, I may have seen it with NB 16. The vertical scroll bar in the output window is stuck at a fixed size. If the output area is made taller the scroll bar starts at the top and ends short of the bottom. If the output area is made shorter, the end will be pushed off the bottom, sometimes hiding the "thumb" completely. This is happening only in the main output pane when I debug the application. Other panes of the output tab, like the "Debugger Console", and Mercurial output don't show this problem.
This is on macOS with FlatLaF Dark, JDK 17.0.6. Scott