Turn your Instant Pot on to saute mode. Once heated, add bacon and cook until browned and crispy, about 6-8 minutes. Remove the bacon and set aside on a paper towel-lined plate. Discard any excess bacon grease remaining in the Instant Pot.
Add olive oil. Once heated and shimmering, add onion, celery, and garlic to the Instant Pot. Cook until the onion is slightly softened and translucent, about 2-3 minutes.
Add clams and clam juice, potatoes, broth, thyme, and salt. Stir to combine and close the Instant Pot lid. Cook at high pressure on manual mode for 5 minutes. Allow to naturally release for an additional 5 minutes, then open the vent to release any additional pressure.
Turn on saute mode. In a medium-sized bowl, whisk together the milk, heavy cream, and cornstarch. Add to the Instant Pot and stir to combine. Stir occasionally until slightly thickened, about 3-4 minutes.
Top with bacon, parsley, black pepper, and oyster crackers. Serve immediately.