[In Windows] By default, Zoom hides the Zoom toolbar when a user is sharing their screen. If you need to access the chat function while screen sharing, first look for the green tab with the Meeting ID on the screen. This is where the toolbar is minimized – you can make it appear by moving the mouse around.Click ‘More’ and then ‘Chat’ (the top option; shortcut is Alt+H) to open the pop-out chat window. [Windows keyboard shortcuts]
No-one can see what you are typing in your Chat, as Zoom only lets you share one screen at a time.
Note: The version of the app for smartphones and tablets does not allow users to chat while sharing their screen.