Since 2017, you can no longer connect iCloud to your normal data. Now you need to create an application-specific password for all applications that want to use your iCloud calendar. Do the following:

  1. Go to the following address and log in with your Apple iCloud data:

  2. In the overview you can see all application specific passwords under "Login and Security" at the bottom right tile "Application Specific...". Click on "Create password" at "Application specific passwords".
  3. Give the password a name e.g. "Calenso"

  4. Now you will be shown code in the format XXXX-XXXX-XXXX-XXXX. Copy this code and paste it in step 5 of this guide.

  5. Done!