Preheat your oven to 325°F (165°C). Line a 12-cup muffin tin with paper liners. In a medium bowl, stir together the graham cracker crumbs, 6 tablespoons of melted butter, 3 tablespoons of granulated sugar, and 1/4 teaspoon of cinnamon until the mixture resembles wet sand. Press about 2 tablespoons of this mixture firmly into the bottom of each muffin cup to form a compact crust.
Bake the crusts for 5 minutes. Remove from the oven and set aside to cool slightly. Reduce the oven temperature to 300°F (150°C).
In a large bowl, use an electric mixer to beat the softened cream cheese and 1/2 cup of granulated sugar on medium speed until completely smooth and creamy, about 2-3 minutes. Beat in the sour cream and vanilla extract until just combined. Add the eggs one at a time, beating on low speed after each addition until just incorporated; be careful not to overmix.
In a small separate bowl, toss the finely chopped apples with 1/2 teaspoon of cinnamon and 2 tablespoons of brown sugar. Gently fold the apple mixture into the cream cheese batter until evenly distributed.
Divide the cheesecake batter evenly among the 12 prepared crusts, filling each cup nearly to the top. Prepare the oat topping by combining the oats, flour, 1/4 cup brown sugar, and 1/4 teaspoon of cinnamon in a bowl. Use a pastry cutter or your fingers to cut the 3 tablespoons of cold cubed butter into the oat mixture until it forms coarse crumbs. Sprinkle the topping evenly over each cheesecake.
Bake for 20-25 minutes, or until the edges are set but the centers still have a slight jiggle. Allow the cheesecakes to cool completely in the pan on a wire rack, then refrigerate for at least 4 hours, or overnight, until fully chilled and set.