Set Instant Pot to 'saute' on 'high'. Once hot, add chopped bacon and cook just until crispy. Using a slotted spoon, transfer cooked bacon to a paper towel-lined plate and pour off all but 1 tablespoon bacon fat.
Add sweet onion, bell pepper, and garlic to the pot; saute for 3 minutes, stirring frequently.
Add diced chicken and frozen corn; saute for an additional 4 minutes, stirring often.
Turn off the Instant Pot. Add chicken broth, potatoes, salt and pepper.
Close and seal the Instant Pot, making sure the vent is in the 'sealed' position. Set the Instant Pot to 'pressure cook' on high for 30 minutes.
Meanwhile, whisk the cornstarch and milk. Set aside.
After 30 minutes, turn the Instant Pot off and allow the pressure to release on its own.
Set the appliance to 'saute' on 'low'. Stir in the milk mixture.
Cover and let sit 10 minutes.
Turn off the Instant Pot and portion soup into bowls.
Swirl in a tablespoon of cream or half-and-half, if desired.
Garnish with bacon and green onions. Season with additional salt and pepper to taste.