Navigate to the calendar month view. Add a user event or (and) a group evento to the calendar. Grab the link of the "ical" icon. Open a fresh new browser without an active moodle session. An option is to open a private browser window. Enter the ical Link in the browers. Check if the ical is downloaded and the added user event is in the ical file. Alternative Testing for step 4-6 is to add the Ical link as a internet calendar in your fresh opened outlook an check if the user event is visible in the calendar. It is important for testing, that there is no active valid moodle session in the browser or outlook.