Using a food processor or blender, blend gingersnaps into a fine powder for crust. Add flour and blitz to process together. Add melted butter and blitz a few times to combine.
Line a 7" springform or push pan with parchment paper. Press crust mixture down into the bottom of the pan. (If you want crust that goes up the sides, double the crust recipe.) Place in freezer to chill.
For the cheesecake filling:
In a medium bowl, mix together cream cheese, sugar, flour, sour cream and seasonings. Blend together until creamy and smooth.
Add eggnog and eggs one at a time, mixing just enough to make them disappear into the mixture. Do not over mix! Pour batter into the prepared and chilled crust.
Cover pan with foil. Add 1 cup of water to the inner pot and place pan on trivet. Close and lock the lid, turning the steam release valve to closed. Press Beans/Chili and adjust time to 25 minutes (high pressure.)
After cooking cycle is done, allow a full natural pressure release (about 10 minutes.) Carefully remove the pan from the inner pot and place in the refrigerator to cool overnight. There should be some jiggle in the middle of the cheesecake. It will firm up as it chills.
For the topping:
Add chilled heavy cream, powdered sugar and vanilla to a bowl. Mix on high until peaks just start to form.
Add chilled eggnog one tbsp at a time, continuing to mix until stiff peaks form. If desired, add a dash of cinnamon and nutmeg while mixing to punch up the eggnog flavor.
Spread topping over chilled cheesecake and serve immediately or return to the refrigerator until ready to serve. Garnish with ginger snap crumbles if desired.