I'm running iOS 13.4.1 on an iPhone SE (original version). There is no default calendar associated with my Calendar app. As a result I cannot add new events because the "+" button is greyed out. The only calendars that show up are the US Holidays and Birthdays calendars. I have tried restarting my iphone, and also deleted/reinstalled the Calendar app. I never tried using the Calendar app until recently, so I don't know if this problem existed in previous iOSs. Does anyone have some suggestions on how to get a default calendar to show up?