Combine flour, butter, and white sugar in a bowl. Beat with an electric mixer on low speed, scraping bowl often, until crust mixture resembles coarse crumbs. Press into the bottom of an 8-inch square baking pan.
Bake crust in the preheated oven until crust is set but still pale, 12 to 17 minutes.
Combine brown sugar, eggs, 1/2 teaspoon rum extract, and salt in a bowl. Beat with an electric mixer on medium speed, scraping bowl often, until well-blended. Stir in pineapple, coconut, and macadamia nuts. Spread filling over hot crust.
Bake in the preheated oven until filling is set and top is lightly browned, 25 to 30 minutes. Let cool completely, about 25 minutes.
Whisk 5 teaspoons reserved pineapple juice, confectioners' sugar, and 1/2 teaspoon rum extract together in a small bowl to make glaze.