I have never had issues adding the closures for the Great North Run but since the updates and changes to Waze for cities I am unable to add as the site as the area covered is more than 12 miles (it’s a half marathon so kind of gives the game away it will be 13.1milea)
If it covers too large an area for the polygon I would suggest just using the whole city as the impacted area. It seems that’s how the impact area was configured for the 2025 event.
What is the error you are getting when leaving it as-is? If the closures are attached to the event regardless of the impact area, drivers should still be notified in advance. Unfortunately it’s a limitation of the system that we can’t create polygons or impact areas that large.