Combine blueberries, pineapple chunks with juice, and 1 1/2 teaspoons flour in a saucepan over medium heat; cook, stirring frequently, until mixture thickens, about 5 minutes. Spread mixture into an 8-inch baking dish.
Preheat oven to 350 degrees F (175 degrees C).
Combine 1 cup flour, oats, brown sugar, cinnamon, and sea salt together in a bowl; mix in butter until topping is crumbly. Sprinkle topping over blueberry mixture.
Bake in the preheated oven until topping is lightly browned, 30 to 35 minutes.
