Hmm, the GPU is 10 years old. The docs say "OptiX-accelerated raytracing requires Nvidia RTX or Turing GPU, or newer." And the K3100M is Kepler, not Turing. So you might be out of luck for Optix.

Restart Poser, then pick the non-Optix GPU option. Does it work? Note that it will not work if you already got an Optix error and did not restart Poser, you need to restart Poser to clear the error.