Preheat the oven to 350°F (175°C). Lightly grease a 9x13-inch baking pan with cooking spray, then line it with parchment paper, leaving a small overhang for easy removal.

In a medium mixing bowl, combine the graham cracker crumbs and melted butter. Stir with a fork until the crumbs are evenly coated and the mixture holds together when pressed.

Transfer the crumb mixture into the prepared pan. Press it firmly and evenly into the bottom using your fingers or the back of a flat-bottomed measuring cup.

Pour the sweetened condensed milk evenly over the graham cracker crust, spreading it gently with a spatula to reach the edges.

Sprinkle the chocolate chips evenly over the milk layer, followed by the butterscotch chips, chopped pecans, and shredded coconut. Gently press the toppings down with your hand or the back of a spoon to help them adhere.

Bake for 30 to 35 minutes, or until the edges are lightly golden and the top appears set. If desired, sprinkle flaky sea salt over the surface immediately after removing the pan from the oven.

Allow the bars to cool completely in the pan on a wire rack. Once firm, use the parchment overhang to lift them out of the pan. Slice into 24 squares using a sharp knife. For cleaner cuts, chill the bars for 1–2 hours before slicing.