Apple Mac
To share a window or your entire screen on Mac your browser needs to be authorised to do this in your System settings. To enable this:
Open your System Settings
In the side panel, select Privacy & Security
In Privacy & Security, scroll down and select Screen & System Audio Recording
Here you should be able to see the browser you were using and toggle your permissions to on. For example in the screenshot below, to enable screen sharing on Google Chrome, you just need to click the toggle to set it to on.
Restart your browser and return to the study.