Add the flour, oats, sugar, cinnamon and salt to a bowl and mix together with a fork until combined.
Using your hands, add the butter to the dry ingredients and crumble the oat mixture together with the butter until the mixture resembles coarse crumbs.
Add the topping over the fruit mixture in the pan, making sure it covers the fruit mixture evenly.
Cover the pan with a double layer of aluminum foil, folding the sides of the foil tightly around the edge of the pan to form a seal.
Pour 3/4 cup of water into the bottom of the Instant Pot, place the pan on a trivet and lower it into the Instant Pot. Close the lid and turn the valve to sealing, setting the Instant Pot to cook on high pressure for 17 minutes.
Once the 17 minutes is up, release the pressure manually (quick release) then remove the pan from the Instant Pot. Remove the foil lid immediately and let the apple crisp cool in its pan on a wire cooling rack for about 10-15 minutes before serving warm with a scoop of vanilla ice cream.