Best/safest exterior cleaning agent for stubborn, hardened pollen?

Simbionic

For 2021 Boondock Tab400. 

BjoLiz

Try giving the area a light spray of Simple Green solution, letting it sit a few minutes, then washing it off.  Follow with a coating of a good fiberglass wax like Maguire's or a similar major brand that is specifically labeled for use on fiberglass boats, cars, etc.