Anaconda navigator only showing one python version

I had the same issue and was hoping there would be an answer here. I finally found the following which directly answers your question. Thanks for asking!

https://docs.conda.io/projects/conda/en/latest/user-guide/tasks/manage-python.html

Specifically, do the following:

Installing a different version of Python. Create the new environment:

To create the new environment for Python 3.6, in your terminal window or an Anaconda Prompt, run:

conda create -n py36 python=3.6 anaconda

You need not go any further. From this point forward, every time you create a new environment, you will see: