Prepare the pan Line an 8×8-inch baking pan with parchment paper, leaving overhang on two sides for easy lifting later.
Make the crust Stir graham cracker crumbs, sugar, and melted butter in a medium bowl until the mixture looks like wet sand. Press it firmly and evenly into the bottom of the prepared pan. Chill the crust while you make the filling.
Beat the cream cheese base In a large bowl, beat softened cream cheese and powdered sugar with an electric mixer on medium speed until completely smooth and free of lumps, about 2 minutes.
Add pumpkin and spices Beat in pumpkin puree, vanilla, cinnamon, ginger, nutmeg, cloves, and salt until fully combined and the color is even. Scrape the bowl as needed.
Whip the cream In a separate cold bowl, whip the heavy cream on medium-high speed until soft peaks form. The cream should hold its shape but still look slightly soft.
Fold and assemble Gently fold the whipped cream into the pumpkin mixture with a spatula until no white streaks remain. Spread the filling evenly over the chilled crust and smooth the top.
Chill until set Cover the pan and refrigerate at least 4 hours, or overnight for the firmest slices.
Slice and serve Lift the bars out using the parchment overhang. Cut into 16 squares with a sharp knife wiped clean between cuts. Add optional topping if desired.