Preheat oven to 325F and line a 9x9 pan with parchment paper.
Simmer the raspberries, 2 tbsp powdered allulose, and lemon juice in a small saucepan for 5 minutes, mashing until thick and jammy. Strain out seeds if desired and let cool.
Whisk together melted butter, melted chocolate, 2/3 cup powdered allulose, eggs, and vanilla until glossy. Fold in almond flour, cocoa powder, and salt to form a thick batter.
Spread the brownie batter evenly into the prepared pan, reserving 3 tablespoons for the top.
Beat the cream cheese with 1/3 cup powdered allulose until smooth, then beat in the egg and vanilla until silky.
Pour the cheesecake layer evenly over the brownies. Dollop the remaining brownie batter and raspberry sauce on top in spoonfuls.
Swirl gently with a toothpick to create dramatic marbled patterns across the surface.
Bake for 32 to 36 minutes until the cheesecake is set with just a slight jiggle. Cool fully, then chill 2 hours before slicing.