Might as well take go to Martha’s Vineyard. You could do a day trip and take the ferry over from Woods Hole, MA on the Cape (Woods Hole has the best lobster rolls, btw). The town of Oak Bluffs in Martha’s Vineyard is a historically African American resort town. Lots of black people there and black businesses. They also have an African American Heritage Trail you can take around the island to learn about black history there. Lots of cool towns across the island though so you wouldn’t want to just stay in Oak Bluffs. Good seafood and beaches. Moshup Beach in Gay Head is spectacular. South Beach in Edgartown in the most popular. The Inkwell in Oak Bluffs is the famed black beach but there are better beaches around the island, tbh. Lots of food options and you can DM me if you want specifics.
Things are a bit expensive on the island though than on the cape.
If you stay on the Cape, Hyannis is nice and you would want to visit Kalmus Beach. Hyannisport is where the Kennedy compound is located.