I am running Mac OSX 10.5.8. I installed matplotlib using macports. I get some examples from the matplotlib gallery like this one, without modification:
http://matpl
Mac comes with its own python (read from here, which is not the best), I would suggest just a clean install of some Python 3.7 or so along with Anaconda and then introduce them as interpreters to PyCharm. anything will work fine and you wont need to add ad-hoc solutions like "backend: MacOSX" or so.