My guess is that you haven't installed the support packages listed on the first documentation page to which you linked.
"Quantization of a neural network requires a GPU, the GPU Coder™ Interface for Deep Learning Libraries support package, and the Deep Learning Toolbox Model Quantization Library support package. Using a GPU requires a CUDA® enabled NVIDIA® GPU with compute capability 6.1 or higher."
To obtain the Deep Learning Toolbox Model Quantization Library support package:
- Go to the Home tab on the Toolstrip.
- In the Environment section click the Add-Ons button (the three colored squares arranged in a triangle.)
- Search for "Deep Learning Toolbox Model Quantization Library" in the Add-On Explorer.
- Open the result.
- Click the Install button on the right side of the window.
If you haven't already installed it you will need to obtain the GPU Coder™ Interface for Deep Learning Libraries support package in the same way. Only step 3, what you search for, is different. [Or since you already have the Add-On Explorer open, start at step 3.]