In a food processor crush 3/4 walnuts until they are fine crumbs. Then mix in melted butter, flour, and 1/4 cup sweetener.
Grease pan well and then pack crust mixture into bottom of the pan. Set pan in the freezer.
Add cream cheese, vanilla, extract, juice from lemon and zest from lemon in food processor (or mixer) and blend.
Now add in the eggs and sweetener and blend again. Make sure not to over blend as we don't want to add a lot of air.
Pour mixture into chilled crust.
Place the trivet into the inner pot of the Instant Pot. Add one cup of water.
Cover top of pan with foil and pinch around the edge of pan.
Carefully put the pan inside the pot on the trivet.
Place the lid on and make sure the valve is on sealing. Push manual (high pressure) and add a cook time of 27 minutes.
When it beeps that it is finished, open valve for quick release. When totally vented, carefully use hot mitt or tongs to remove the pan from the pot and set on the counter.
Remove foil from pan and allow to cool for 30 minutes. Then place in the fridge to cool the rest of the way.
When totally cooled, remove from pan. Top with cool whip and a few crushed walnuts.