Hello,
In discord or any other application, the screen sharing for a specific window does not show anything. I have seen this in Discord and while using Google Meet on firefox, chrome, and brave browsers. The entire screen sharing works fine.
In OBS Studio Window Capture, the window titles are not shown. (Screeshots Included)
What Desktop environment are you on? Discord screensharing used to - not sure if it still does - be troublesome when run under Wayland, so if that is the case for you, it is perhaps worth attempting the same under an X session.