This video discusses how to convert materials from the built-in Cycles Renderer in Blender™ to Radeon™ ProRender materials. It also handles converting lights!
The converter functionality seems to be missing from Blender v2.81.16
This was for the older version of the plugin. Now it converts thing on the fly.
How does it handle instances where ProRender doesn't support something? How do you get back to other renderer's nodes?