Line an 8×8 or 9×9 inch square baking pan with parchment paper, leaving overhang on the sides for easy removal.
In a medium bowl, combine graham cracker crumbs, melted butter, sugar, cinnamon, and salt. Mix until the crumbs are evenly moistened and resemble wet sand.
Press the mixture firmly into the bottom of the prepared pan using the bottom of a measuring cup to create a compact, even layer. Place in the refrigerator to firm up while preparing the filling.
In a large bowl, beat the softened cream cheese and sugar with an electric mixer until smooth and fluffy, about 2 minutes.
Add the sour cream, lemon juice, vanilla extract, and cinnamon, beating until fully incorporated.
Gently fold in the whipped heavy cream using a spatula, maintaining as much air as possible for a light, mousse-like texture.
Spread the cheesecake filling evenly over the chilled crust using an offset spatula. Smooth the top as much as possible. Refrigerate for at least 2 hours or until set.
In a medium saucepan over medium heat, melt the butter. Add diced apples, brown sugar, cinnamon, and nutmeg.
Cook, stirring occasionally, for 7-8 minutes until apples are softened but still maintain some texture.
Add the cornstarch slurry and cook for an additional 1-2 minutes until the mixture thickens. Remove from heat and let cool completely.
Once the apples have cooled to room temperature, spread them evenly over the set cheesecake layer.
Drizzle with caramel sauce, reserving some for serving. If using salted caramel, sprinkle a pinch of sea salt over the top.
Return to the refrigerator for at least another 2 hours or preferably overnight.
To serve, lift the cheesecake out of the pan using the parchment overhang. Cut into 16 squares with a hot knife, wiping the knife clean between cuts for neat edges.