In your Instant Pot, turn on the saute function and add the chopped bacon. Let it start rendering, but do not let it become crispy.
Add the butter and the onion and saute for a few minutes until the onions become translucent. Add the celery and saute for a few minutes.
Turn off the saute function. Add the clams, bone broth, thyme leaves, potatoes and heavy cream. Mix everything together well. Close the lid and the vent, and set to pressure cook for 5 minutes. Let the steam naturally release for 5 minutes, then release the vent. Once all the pressure is gone, remove the lid and turn the saute function back on again.
Take ⅓ cup of the soup and mix it with the arrowroot, and then stir it very well back into the soup. Turn the saute function off, and serve hot!