Set the Instant Pot to sauté. Add the oil, onion, and bell peppers, and sauté about 4 minutes until softened. Scrape the bottom of the pot clean.
Add the broth, potatoes, corn, salt, and pepper. Stir well.
Lock the lid, set the valve to sealing, and cook on high pressure for 6 minutes.
Meanwhile, melt the butter in the microwave. Whisk in the flour until smooth, then whisk in the milk to make a roux.
Let the pressure release naturally for 10 minutes, then quick release any remaining pressure.
Stir the roux into the chowder. Turn on sauté and simmer 2 to 3 minutes until thickened. Taste and adjust seasoning.
Serve topped with bacon, cheddar, or sour cream.