That is really weird. It should detect your GPU automatically. I would double check whether this is an issue with the game or with ComfyUI. You can manually run ComfyUI by going to data/services/comfyui/ and click run_nvidia_gpu_bat. It should open a GUI in your browser, drag in the following workflow:
https://github.com/venus-uni-dev/venus-uni-comfyui
And click run. You should be able to run it without having to download any of the models since it'll find the ones you downloaded through the game. The outputs should appear in data/services/comfyui/ComfyUI/output
If it's still not using your GPU there, I'd look up online about your GPU and ComfyUI and see if anyone else is having similar issues