Combine the graham cracker crumbs, sugar, cinnamon, and salt in a medium bowl. Pour in the melted butter and stir until the mixture resembles wet sand.
Press the mixture firmly into the bottom and up the sides of a 9-inch pie dish. Use the bottom of a measuring cup to create an even, compact layer with a smooth finish.
Bake the crust at 350°F for 8-10 minutes until lightly golden and fragrant. Allow to cool completely on a wire rack before filling.
In a large bowl, beat the softened cream cheese until completely smooth with no lumps – about 2 minutes on medium speed.
Add the pumpkin puree, brown sugar, vanilla, pumpkin pie spice, and salt. Beat until thoroughly combined and silky smooth, scraping down the sides of the bowl as needed.
In a separate chilled bowl, beat the heavy cream until it begins to thicken. Gradually add the powdered sugar and continue beating until medium-stiff peaks form.
Using a rubber spatula, gently fold one-third of the whipped cream into the pumpkin mixture to lighten it. Then, carefully fold in the remaining whipped cream using a figure-eight motion until no visible streaks remain.
Spoon the pumpkin mousse into the cooled graham cracker crust, creating a slight dome in the center. Smooth the top with an offset spatula.
Cover loosely with plastic wrap (avoid touching the surface) and refrigerate for at least 4 hours or overnight.
Just before serving, whip the cream for the topping with powdered sugar and vanilla until stiff peaks form.
Pipe or spread the whipped cream over the chilled pie and dust lightly with cinnamon or nutmeg for an elegant finishing touch.