Syncing your google calendar with the elementary OS Calendar application is super simple, but not obvious. I had initially tried, then noticed that it wasn’t working and forgot about it. After all, I normally always use calendar.google.com on a pinned browser tab on any computer or OS that I use.
First of all, create a new calendar of “Google” type, enter your google username (no need for “@gmail.com”):
You will be then asked for a password:
Go to your google account settings and under the “Signing in to Google” section, you will find an “App passwords” setting.
Generate a new password for the elementary Calendar, then use it in the “Calendar authentication request” dialog.
And that is it.