Calendar event is shown 1 month later

Hi, I created a calendar with a hardcoded event on the Nov. 24th, 2020:

    inputEl: '#calendar-addFlight-date',
    dateFormat: { 
      weekday: 'short',
      month: 'long', 
      day: '2-digit', 
      year: 'numeric'
    closeOnSelect: true,
    value: [new Date()],
    maxDate: new Date(),
    direction: 'vertical',
    events: [
        date: new Date(2020, 11, 24),
        color: 'red',

But, somehow the event on the calendar is shown at Dec. 24th, 2020 (one moth later):

Have I overlooked something?

11 is december, months start at 0 in javascript