When sharing your screen, one common interaction is the so-called "infinity mirror" effect. This happens when you share your (entire) screen, and your Lessonspace space is open and visible in the screen share.
If you click Okay, I Understand, you'll see this infinity mirror effect:
The reason this effect happens is that you're sharing the screen that's showing the shared screen which creates an infinite loop of screen shares.
There are two ways to prevent this:
Make sure that you move to another window or tab (so that the Lessonspace Space isn't visible in the area you're sharing); or
Choose to share an individual application window or tab. This is demonstrated in the video below.