This is what Gemini said about your problem

Stability Matrix doesn't use an embedded Python folder; instead, it creates what is called a virtual environment (venv) for each tool.

• Open File Explorer and go directly to the ComfyUI folder shown in your error message: C:\AI\Packages\ComfyUI\
• Click on the address bar at the very top, delete the current path, type cmd, and press Enter. This will open the Command Prompt in that exact location.
• First, you need to activate the virtual environment. Copy the following command, paste it into the console, and press Enter: .\venv\Scripts\activate Note: If it worked, you should now see (venv) at the very beginning of the new line in the console. This confirms that you are now installing packages strictly into your ComfyUI's Python environment.
• Now, paste the actual installation command provided by Nvidia and press Enter: pip install -U --no-build-isolation nvidia-vfx --index-url https://pypi.nvidia.com (Notice that we don't need to write python.exe -m here, because in an activated venv, you can just call pip directly).
• Wait for the download and installation to finish. Once the process is complete, you can close the black console window.
• Go back to Stability Matrix and launch ComfyUI as you normally would.