Preheat oven to 350°F. Mix crushed pretzels, melted butter, and 3 tablespoons sugar in a bowl until well combined, then press firmly into the bottom of a 9x13-inch baking dish.
Bake the pretzel crust for 10 minutes, then remove from oven and let cool completely on a wire rack.
In a large bowl, beat softened cream cheese with 1 cup sugar using an electric mixer until light and fluffy, about 2-3 minutes.
Gently fold the whipped topping into the cream cheese mixture until smooth and well combined, then spread carefully over the cooled pretzel crust, making sure to seal all the way to the edges.
Refrigerate the dish while you prepare the strawberry layer.
Dissolve both packages of strawberry Jello in 2 cups of boiling water, stirring for 2 minutes until completely dissolved, then add 1 cup cold water.
Stir in the thawed strawberries with their juice, then refrigerate the mixture for about 20-30 minutes until it thickens to the consistency of egg whites but is not fully set.
Carefully pour the thickened strawberry mixture over the cream cheese layer, spreading gently to cover completely.
Cover and refrigerate for at least 4 hours or overnight until the Jello layer is completely firm before cutting into squares to serve.