C4D R20 is not currently supported, only R21 for now.
To test your GPU, please download and install Standalone OctaneX PR1.1.
You can find it by visiting your personal Downloads area:https://render.otoy.com/account/download_archive.php
Then open Standalone, right click anywhere in the node graph panel, and choose Materials/Metallic, to create the material node.
Now right click on the node and choose Render.
Then please share a screenshot of the Standalone interface thanks.