From Onset Developer Wiki

This describes the game console parameters.

Switch Description
-dev Enables the development mode. Currently this enables file logging of Lua errors and more. File is to be found under %appdata%..\Local\Horizon\Logs\DevLog.txt
-ConnectAddress= Connects to a specific server by ip or hostname.
-ConnectPort= Specifies connect port.
-ConnectPassword= Specifies server password.
-dx12, -dx11 (default) Specifies DirectX RHI version.
-windowed Starts game in windowed mode.
-fullscreen Starts game in fullscreen mode.