Install the following apps if you don’t already have them:
Install Evolution and Gnome Calendar:
sudo apt install evolution gnome-contacts
We will be using Evolution to set up the iCloud accounts but you will most likely want to use Gnome Calendar as your daily calendar as it offers a minimal, beautiful experience.
That’s it! If all goes well, you should see your calendar entries begin to pop up in Evolution. If you want to set up additional calendars, rinse and repeat the instructions in this section. Once you’ve set up your accounts, fire up Gnome Calendar and enjoy your synchronised calendars in a beautifully minimal interface. Any entries you make in Gnome Calendar will sync to iCloud and, from there, to all of your Apple toys, and vice-versa.