If the grey boxes look like they were formed by Zoom window panels, it is actually a security feature by Zoom to prevent participants from seeing your chat window and whatever settings on Zoom you are doing. Imagine someone sending you private message, seen by all.
If you are using dual monitor, try to shift the panels on the other monitor. Or probably use another device to monitor group chat panel. (Do not join audio if you are using another device, to prevent echo and feedback).
Alternatively, you can:
- Share just that app or window. Example: If you are sharing a video playing on your VLC Player or Quicktime, share just that window.
When you share the entire Desktop Screen, it tries to hide your Zoom panels.
- Disable "Optimize for Full Screen Video clip"
Should not be selecting this unless you are sharing a video. It will reduce the sharpness of your presentation.
Note: Disabling Optimize for Full Screen Video may cause a slight sync issue when you play a video.