If you need to share your screen using a Mac, you must first allow screen sharing in your system preferences. To do so:
Click on the Apple Menu and select System Preferences
Search for Security & Privacy
Select the Privacy Tab and then Screen Recording (Click on the lock to make changes).
Check the box next to the app you want to use to record contents of your screen.
Once the app is selected, click on "Quit Now", close and reopen your browser, and rejoin the link.
Updating your system preferences may require a restart of your computer.