Turn your Instant Pot to sauté, heat oil and cook bacon in batches until crispy. Remove and set aside.
Cook chopped onion for about a minute and garlic for about 30 secs.
Add clams with juice to the pot. Add the bacon back to the pot with all the other ingredients except the sour cream, cream, and cornstarch.
Cover and set to manual pressure / high pressure for 10 mins, until potatoes are tender. Allow for a natural pressure release.
Turn the pot back on to sauté mode. In a separate cup, mix the cream and cornstarch until no longer lumpy and add to Instant Pot.
Add sour cream to the pot and stir to combine.
Use a potato masher to mash the potatoes in the chowder, leaving some lumps. Let simmer for a few mins.
Turn off, garnish with bacon and green onions, and serve hot.