Max, I vacation on Newfound every July and I have caught most of my fish around Mayhew Island. Its on the southeast side of the lake. The backside of the island is all boulders. Depth is about 15 - 20+ feet.
I've also caught fish around the 2 islands near the boat launch at wellington state park.
PM me if you need more detail.
I fish in mid July but I've had luck on deep diving cranks, tubes, craws, spinners. White tubes dipped in chatreuse die are my go to.