Zoom is designed to have a very simple but yet useful interface. We have 2 display modes - video layout and screen sharing layout.
In the video layout, Zoom is optimized for video viewing and desktop viewing. To go full-screen, double click on the screen or click on the Full Screen icon up at the top right corner.
In the screen sharing layout, Zoom automatically switches to full-screen to optimize the document or presentation view. To exit full-screen, double click or hit Esc.
You can change your settings for full screen in your Zoom client settings, under the General tab.