Press the Saute button on your Instant Pot and let it heat for a minute. Add the bacon pieces and cook, stirring occasionally, until they are crispy and the fat has rendered out, about 5 minutes. Use a slotted spoon to scoop the bacon onto a paper-towel-lined plate and set it aside. Leave the bacon fat in the pot.

Add the diced onion and celery to the pot. Cook in the bacon fat, stirring every minute or so, until the onion is soft and translucent, about 4 minutes. Add the garlic and stir for 30 seconds until fragrant. Press Cancel to turn off the saute function.

Add the cubed potatoes, bottled clam juice, chicken broth, thyme, bay leaf, salt, and pepper to the pot. Pour in the reserved liquid from the canned clams as well. Give everything a stir. Secure the lid, make sure the vent is set to Sealing, and pressure cook on High for 5 minutes.

When the cook time is done, carefully do a quick release by turning the vent to Venting. Once the pressure pin drops, open the lid. The potatoes should be fork-tender. Remove and discard the bay leaf.

In a small saucepan over medium heat, melt the butter. Whisk in the flour and cook for 1 minute, stirring constantly, until the mixture smells slightly nutty and looks pale golden. Slowly whisk in the heavy cream a little at a time until smooth. Pour this cream mixture into the Instant Pot and stir to combine.

Press Saute on the Instant Pot. Add the drained canned clams and stir everything together. Cook for 3 to 4 minutes, stirring gently, until the chowder thickens enough to coat a spoon. Do not boil it hard or the clams will get rubbery. Taste and adjust salt and pepper.

Ladle the chowder into bowls and top each one with the reserved crispy bacon. Serve immediately with oyster crackers or a thick slice of crusty bread.