As seen in "Olaf's Frozen Adventure" there was a Christmas event that took place in Arendelle, the first such celebration since the gates were opened. I would like to ask if "Christmas in Arendelle" (title is conjectural) can exist as a page or if that is unnecessary?
You can always start the page. I don't think anything has been said against starting one, but the focus would have to be on the event itself and what took place within it, and not describing what has already been separately mentioned on say character pages, regarding their personal feelings within the event. Refer to other event pages and see if you can construct a page on this event with the same format and writing technique.