It seems that you have to put the following in your (at the end) .bash_profile or .szhrc:

eval "$(pyenv init -)"

A good source for this was: pyenv don't switch between python versions on macos #1446. Also, there is some good information on Catalina, where Apple switched to zsh as the default shell. One user cseder has a lot of good information on what you need (and how you should do it) when/if you switch to zsh. Not there yet on my TDA laptop, so ...

This probably should have been done (or was told to do) after installing it, but either I didn't do it or it got overwritten.