We are sorry for our late reply, due to the latest release of the theme we are getting more traffic than usual. ALso kindly wait until one of our colleagues get back to you if you add another question the system will reset the queue and the thread will go to the end of the queue.
I am not sure what the Latest Add-ons is regarding the Modern Event Calendar, but if you want to add attendees you can use the MEC Single Sidebar Items widget and assign it to MEC SIngle SIdebar widget position. There you will have the option to show the Attendees:
Attendees are available only if you use the Booking module. For more information kindly read this article: