Preheat oven to 375°F. Lightly spray a 7-inch springform pan with nonstick cooking spray.
To make the crust:
Process Oreo cookies in a food processor to fine crumbs. Add 4 tbsp. of melted butter and process for a few seconds, until combined.
Using your fingers, press the crust mixture into the bottom of the prepared 7-inch springform pan and about a 1⁄2-inch up the sides of the pan.
Bake in the pre-heated oven for 10 minutes. Set aside.
To make the filling:
While the crust is baking, put cream cheese and sugar in a large bowl and mix using an electric hand mixer (or a stand electric mixer) until smooth.
Add in pumpkin pie spice, flour and salt and mix till combined.
Add the eggs, one at a time, and mix again just until combined.
With a spatula, mix in the pumpkin purée, sour cream (or yogurt) and vanilla extract, until combined.
Finally stir in four crushed Oreo cookies into the batter.
Pour the batter into the pre-baked crust. Tap the pan gently on a table top or kitchen counter to get rid of any air bubbles. Cover with aluminum foil
Place a trivet into the inner pot of your instant pot and pour in 1 cup of water. Put the springform pan on top of the trivet. If your pressure cooker didn't come with a trivet, just use a sling made out of aluminum foil.
Close the lid and turn the valve to “seal”. Pressure cook on high pressure for 40 minutes. Allow the pressure to release naturally for 15 minutes, then do a quick release
Remove the cheesecake and set on a wire rack. If there is any moisture on the top of the cheesecake, just mop with a paper towel. Leave the cheesecake to cool at room temperature for 45 minutes.
Cover cheesecake with plastic wrap and refrigerate for at least 6 hours, preferably overnight.
When ready to serve: top cheesecake with whipped cream, some crushed Oreos, and chocolate syrup, if preferred.