Set the Instant Pot on SAUTE function & set it on NORMAL heat. Add oil. When the oil becomes moderately hot gently release the chopped bacon and saute until lightly crispy stirring frequently. You'll have lots of bacon fat. You may discard it or use it in the next step.
Now, add the onion and celery and saute until the onions begin to become translucent and soft. Add salt to quicken the process.
Reduce the heat to LOW. Add the butter and allow it to just melt. Than, add the flour and stir briskly for 30 seconds to form a quick roux.
Drain the clams from the cans & reserve the clam juice. Set aside the clams.
Pour the clam juice and the chicken stock into the Instant Pot steel insert and de-glaze the pot very well with the help of a spatula scraping the sides and the bottom of the pot. There should not be any food particles stuck at the bottom of the pot. This will prevent the BURN error.
Now, add the seasonings except the crushed black pepper and give everything a quick stir.
Add the diced peeled potatoes and give everything a quick stir. Bring the liquids to a gentle simmer. Stir to prevent the roux from sticking at the bottom of the pot.
CANCEL the SAUTE function. Close the lid, seal the valve and PRESSURE COOK on HIGH for 3 minutes.
Once, the pressure cooking cycle is over do a quick pressure release (QPR) by manually moving the valve from the SEALING to the VENTING position. When the metal pin drops open the lid carefully.
TURN OFF the Instant Pot and add the heavy cream (**read NOTES below). Give everything in the pot a quick stir.
Now, add the clams and mix well. Hit the SAUTE function & set it on LOW settings. Bring the chowder to a gentle simmer. You can skip this step as well.
Check for seasoning and add crushed black pepper. Served hot and top with crispy fried bacon, chopped fresh parsley and oyster crackers. Dig in!