In the output settings you can add as many outputs as you would like.
You can enable or disable each individual output. It's recommended to have different colors for different outputs.
How to use
When you have more than one output active you will get some buttons over the output preview on the right side, where you can click on them to change the currently active output window, or hold CTRL/CMD to select multiple. And right click any of them to show or hide individual windows.
When starting a show, or clearing layers it will only change the selected output windows.