Set the Instant Pot to saute. Add in butter and let it begin to melt. Toss in onion, garlic, celery, carrots, mushrooms, and bell peppers. Cook for 3-5 minutes, stirring occasionally.
Next toss in the potatoes, vegetable broth, beans, corn, fresh sage, rosemary, and salt and pepper. Change the Instant Pot to the manual setting; adjust pressure to high. Secure the lid on and turn the valve on top to the sealing. Cook this for 6 minutes.
Once timer goes off, carefully release the valve (manual release). I use a towel or pot holder for safety!
Mix corn starch with 2 Tbsp. water and whisk it in the soup with the milk to thicken the soup. Set Instant Pot back to saute mode. Whisk and bring to a boil. Top with cheese, jalapeños, bacon or your favorite chowder toppings! Enjoy!