Line a 9x9-inch square baking pan with parchment paper, leaving overhang on two sides for easy removal. In a medium bowl, mix graham cracker crumbs, melted butter, and granulated sugar until the mixture resembles wet sand.

Press the crumb mixture firmly into the bottom of the prepared pan using the bottom of a measuring cup to create an even, compact layer. Refrigerate while you prepare the filling.

In a large mixing bowl, beat the cream cheese with an electric mixer on medium speed until completely smooth and fluffy, about 2 minutes. Scrape down the sides of the bowl.

Add the powdered sugar and vanilla extract to the cream cheese, then beat on low speed until fully incorporated and silky, another 1-2 minutes. Set aside.

In a separate chilled bowl, whip the heavy cream on high speed until stiff peaks form, about 3-4 minutes. The cream should hold its shape when you lift the beaters.

Gently fold one-third of the whipped cream into the cream cheese mixture using a rubber spatula to lighten it, then fold in the remaining whipped cream until no white streaks remain. Be careful not to deflate the mixture.

Spread the cheesecake filling evenly over the chilled crust, smoothing the top with an offset spatula. The layer should be about 1.5 inches thick.

Cover the pan loosely with plastic wrap and refrigerate for at least 4 hours or overnight until the filling is completely set and firm to the touch.

Just before serving, arrange the strawberries, blueberries, and raspberries on top in stripes, rows, or a scattered pattern to create the red, white, and blue effect. Use the parchment overhang to lift the cheesecake out of the pan.

Slice into 12 squares using a sharp knife dipped in hot water and wiped clean between cuts. Serve immediately and store any leftovers covered in the refrigerator.