It seems clear that Airbnb suspended your listing because you allowed a party of 45 people at your listing contrary to your local Covid regulations.
Your choice once you knew these updated regulations were in place was to cancel the booking or host it within the reduced number allowed by the state.
if your guests booked in June they would have known there was a high risk their event might not be able to take place because of Covid restrictions.
it’s irrelevant that the event was outside. That many people travelling to an event, mingling together and the returning to their homes does present a risk to the guests, the areas they travel through and their home communities.
You have only been allowed to have a maximum of 16 guests stay at a property for at least the last two years.