The Viewport enables to you position, scale and rotate your objects in a 3D space, but it isn't an accurate preview of the output. That's why we have the Simulator Window.
The Simulator Window is a separate view for previewing the output of any changes you make in the Viewport and is an accurate representation of what the effect will look like on your device.
The Viewport and the Simulator Window are designed to be used in sync, but if you want to hide either one, you can.
Docking the Simulator Window will maximize it and hide the Viewport. To dock the Simulator Window, click on it to show the buttons and click the third one from the left.
To hide the Simulator window, go to View in the navigation bar and click Hide Simulator.
If you have more than one camera input available (a camera on a laptop and one on a connected monitor, for example) you can choose which one Spark AR Studio uses. To do this, long-press on Video in the Toolbar and select the camera you want to use from the menu.