Combine the frozen mixed berries, granulated sugar, and lemon juice in a medium saucepan over medium heat. Cook for 20 minutes, stirring occasionally and mashing the berries with the back of a spoon as they soften. Continue cooking until the mixture is thick and jammy.

Transfer the jam to a heatproof bowl and refrigerate until completely cool before assembling.

Add the graham crackers to a food processor and pulse until fine crumbs form. Transfer the crumbs to a large bowl and stir in the rolled oats, granulated sugar, and brown sugar.

Pour in the melted butter and mix until all of the dry ingredients are evenly coated and the mixture resembles wet sand.

Firmly press about half of the crumble mixture into the bottom of an 8×8-inch square pan using the bottom of a measuring cup or glass to create an even layer. Place the pan in the freezer while you prepare the cheesecake filling. Reserve the remaining crumble for layering and the topping.

Add the softened cream cheese and granulated sugar to a large mixing bowl. Beat with an electric mixer on medium speed until smooth and creamy, about 2-3 minutes, scraping down the sides of the bowl as needed.

Add the Greek yogurt, vanilla extract, almond extract, and salt. Beat again until fully incorporated and smooth.

In a separate large bowl, beat the cold heavy whipping cream on medium-high speed until stiff peaks form. The whipped cream should hold its shape when you lift the beaters.

Using a rubber spatula, gently fold the whipped cream into the cream cheese mixture in 2-3 additions until no streaks remain. Be careful not to overmix so the filling stays light and fluffy.

Remove the pan from the freezer and spread half of the cheesecake filling evenly over the crust. Spoon half of the cooled berry jam over the filling and gently spread it into an even layer.

Sprinkle about half of the remaining crumble evenly over the jam. Spread the rest of the cheesecake filling on top, followed by the remaining jam.

Finish by sprinkling the rest of the crumble over the top. Cover the pan with plastic wrap and refrigerate for at least 6 hours, or overnight, until the cheesecake is thoroughly chilled and set.

Scoop into bowls using a large spoon or ice cream scoop and serve cold.