Zoom - Viewing participants' video while screen sharing, on a Chromebook

After sharing the screen or application, clicking on the Zoom icon in the shelf at the bottom of your screen (some may refer to it as the Taskbar - which is a Windows thing) does bring up the participants' video where they can be viewed.

Ideally, having a second screen provides a better viewing experience as your screen share can be on one screen and the participants' video on the other.