No dispersed camping on the island, sorry. The Park Service is not opening up the campgrounds in Acadia this year either, but the private ones are open and getting spots shouldn’t be an issue, especially after Labor Day. There are a few state parks, Lamoine is 20 minutes away, but the rest are a few hours (Baxter, Cobscook, Camden, etc). Check out https://www.campwithme.com/ State parks are very popular lately, so book early to get a spot.
No stealth camping in the town is allowed, and Park Rangers actively discourage/patrol and issue tickets freely if they discover campers trying to do so in the park .
Visitation is down this year, and no cruise ships are coming, but Park traffic is up with day visitors, but not like in years past.
FWIW, we live in Bar Harbor and my wife work for the park.
Enjoy your stay here….