In a medium bowl, combine graham cracker crumbs and melted butter. Press the mixture into the bottom of a 9x13-inch baking dish to form the crust.
In another bowl, beat the softened cream cheese, powdered sugar, and vanilla extract until smooth and creamy. Gently fold in 1 cup of whipped topping until well combined. Spread this cream cheese mixture over the graham cracker crust in the baking dish.
In a separate bowl, dissolve the berry-flavored gelatin in 1 cup of boiling water, stirring until completely dissolved. Add 1 cup of cold water and mix well. Allow the gelatin to cool slightly.
Layer the mixed berries evenly over the cream cheese layer. Pour the cooled gelatin mixture over the berries, ensuring they are fully covered.
Refrigerate for at least 4 hours or until the gelatin is set.
Before serving, spread the remaining whipped topping over the top of the gelatin layer. Cut into squares and serve chilled.