Hi. I'm just an admin user... not a developer.. but I think you can find some answers here : https://community.plone.org/t/import-ical-to-plone-5/1655/6
We are using this kind of solution with the public ical link of our Google Calendar (just make sure the share setting are in "Public" mode in Google Calendar) and it's work great.
So we can manage then ours events in our Plone website and display them in a pretty cool widget customized by our provider (Iskra)