Turn your Instant Pot to "Saute". Melt the butter in the pot and add the oats. Stir until the oats are fragrant, about 3 minutes.
Add the apples, vanilla, cinnamon, nutmeg, and water. Stir well. Close the lid and cook on manual, high pressure, for 10 minutes. Use the quick release.
Turn the Instant Pot off and add the brown sugar and raisins. Stir well. If it's watery, let it stand for a few minutes to thicken up.