Does anyone know which specific path introduces Windows 2016 in the Configure Managed Nodes/OS Setup/Version box?
Is it bundled in the new agent installation or a seperate server patch?
It is introduced and bundled in the consolidated installation media of agent 12.01. As a reference you can check the following link:
Make sure to register the OA 12.01 Windows packages in your OMW management server before adding nodes and deploying the agent to them.