Have you tried the following in a cell in the Jupyter notebook in place of your outdated installation command:
%pip install selenium
It is best in a notebook to use the %pip install and %conda install so that installations happen in the correct environments that the notebook uses. See the very bottom of this reply for a link to related information on those new magic commands that make life much easier. Adding the exclamation point sends it out to a shell which looks in your case to be using your Mac Python and not the Anaconda installed environemnt, it seems.