Borked it. Fixed it

 I tried to install Renderman for Blender. There's an issue where the add-on element doesn't work because it can't find the Renderman installation path. The add-on panel gives you about four different methods for finding the path, but none seem to work for me. It's a mess!

I manually created environmental variables. I added and removed the add-on several times with no success.


I gave up.

I started playing with Blender. Every render crashed. I removed renderman, I removed the manually added environmental variables. Nothing fixed the issue. 

I thought back. Hm, you know, I accidentally unticked the cycles add-on in a fat finger moment. I instantly re-ticked it but on checking back I saw that the add-on I see that Cycles was no longer assigned to a rendering method. So no longer set to Optix or CUDA. 

I reenabled Optix. Saved and restarted. All is well...for now.