Preheat your oven to 350°F (175°C). Mix crushed pretzels and sugar in a bowl, then stir in melted butter until evenly moistened.

Press the mixture firmly into the bottom of a 9×13-inch pan. Bake for 8–10 minutes until set and slightly golden. Let cool completely.

In a large bowl, beat softened cream cheese with sugar and vanilla until smooth.

Fold in the whipped heavy cream gently until no streaks remain. Spread this mixture evenly over the cooled pretzel crust. Chill the pan in the refrigerator while you prepare the topping.

In a small saucepan, combine sliced strawberries, sugar, and lemon juice. Cook over medium heat until the berries release juices and the mixture is slightly saucy (about 5 minutes).

In a separate small saucepan, bring the agar-agar and 1/4 cup water to a boil, stirring constantly for 1–2 minutes until fully dissolved.

Remove the agar-agar from heat and stir into the warm strawberry mixture. Let cool slightly, then spoon the strawberries and syrup over the cream layer. Refrigerate for at least 3–4 hours, preferably overnight, until set.

Slice into squares with a warm, dry knife for clean edges. Keep chilled until serving.