A note on the water ratio:
Depending on how thick or thin you prefer your oatmeal, adjust the water ratio accordingly. I find anywhere between 2 to 2.5 cups of water per 1 cup of oats works well. I like my oatmeal a bit runnier, so I use 2.5 cups of water. You can also substitute some of the water for milk, almond milk, oat milk, etc. Be careful if you are using too much milk as it can burn in the instant pot!
I would recommend at least 10 minutes of natural release. Leaving the oatmeal in the pot longer is perfectly fine too!