Preheat oven to 325°F (163°C).

In a mixing bowl, combine graham cracker crumbs, melted butter, and 1/4 cup sugar to form the crust. Press mixture into the bottom of a springform pan.

In another bowl, beat the softened cream cheese until smooth. Add sour cream, 3/4 cup sugar, eggs, and vanilla extract. Mix until well combined.

Gently fold in fresh blueberries, cornstarch, and lemon juice into the cheese mixture.

Pour cheesecake filling over the crust in the springform pan.

In a separate bowl, mix oats, brown sugar, all-purpose flour, and cinnamon (if using) to create the crumble topping. Sprinkle the crumble over the cheesecake filling.

Bake in the oven for 60 minutes or until the center is set but slightly jiggly.

Allow cheesecake to cool, then refrigerate for at least 4 hours or overnight before serving.