In the win10 version of QGIS, you can install extra Python packages with pip commands directed at the QGIS python 3 environment. For example, I've got access to scikit-learn form my QGIS Python console.
What is the equivalent process for a mac?
The sticking point seems to be getting the terminal to point to QGIS's Python 3 environment. In Windows it's just a py3_env command. No luck on MacOS.