Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
I created a new Lion Den this year and the Den Calendar appears in Internet Advancement. I can add events to that calendar. However, when I try to subscribe to the calendar link my calendar software tells me the link could not be found.
We had already had other problems with that Den with the Den Leader not being able to see some of her Scouts. So I tried “fixing” the calendar by making a new Den and moving all the Scouts to it, but that calendar is also broken.
I think there was just a delay in getting it to work. When the link didn’t work I did add a test event and immediately tried to subscribe again. After taking the time to go through those other steps, I guess the system had time to create the calendar. I haven’t checked the documentation for creating a calendar, but it should mention that an event needs to be added and then you might need to wait before the link becomes active.