Cook bacon in the Instant Pot on the saute setting until crispy. Remove bacon and set aside, leaving the grease in the pot.

Add onion to the pot and saute until softened, about 5 minutes.

Add potatoes and clam juice to the pot. Season with salt and pepper.

Close the lid and set the Instant Pot to manual high pressure for 8 minutes. Allow a natural pressure release for 10 minutes, then quick release any remaining pressure.

In a small bowl, whisk together arrowroot powder and cold water until smooth.

Select the saute setting. Slowly pour the arrowroot slurry into the Instant Pot, stirring constantly until the chowder thickens.

Stir in heavy cream and chopped clams. Heat through.

Crumble cooked bacon over the chowder before serving.