All Rendering Engines you see in the PhotoRendering Settings Dialog (Basic Renderer, CineWare by Maxon, Sketch) are CPU-based rendering engines.
The OpenGL Engine is used in the 3D Viewpoint, when you are viewing, editing, navigating your model there. OpenGL is using the GPU, and the following article covers the suggested graphics card for Archicad 24:
I would be interested to know where you read about multi-GPU and Archicad (Nvidia SLI or AMD CrossFire). I do not see any such information in the above article. As far as I know, programs have to be additionally coded to take advantage of multi-GPU hardware, and I am not aware of any such development in Archicad. But I may be wrong, so if you could provide the link to the source of that info, I would like to read it.