Legacy documentation is for v2.0.4 which is deprecated.
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In order for the Operating System to work, you need a device actor placed in world. To create a new device manager, right-click on Content Browser -> Operating System Simulator -> New Device Manager. Keep all the settings at default, drag and drop this actor onto the world and press play. From the log, you will see an ensure condition failed message has appeared. This is because there is no default device assigned to the manager.To fix this and to make things work, enable plugin content and assign a default device that comes with the plugin. You should now be able to boot successfully.