Make sure your liner is in the pot, and then hit the saute button on your Instant Pot.
Add both the chopped bacon & onion to the pot, stirring and cooking until the bacon's cooked and the onion's tender. Add the celery, and cook just one minute more until it too is tender. Hit the 'cancel' button to turn the pot off and end the saute mode.
Pour the broth into the pot, and using a sturdy spoon deglaze the bottom of the pot, scraping up any browned stuck on bits as you do so.
Add the potatoes to the pot, and lightly season with salt & pepper.
Place the lid on the pot, turning to close and set the vent knob to the sealed position.
Hit the 'pressure cook' or 'manual' button, depending on your model, and set to 8 minutes.
Once the soup's done cooking, let it naturally release (sit undisturbed) for 10 full minutes. Quick release the remaining steam, carefully turning the knob to avoid any hot water. You can loosely cover the knob with a damp cloth if you want to avoid any potential starch from escaping with the water vapor.
In a small dish, whisk together the flour and melted butter until the mixture's smooth and no lumps remain.
Once all the pressure's been released open the lid, careful to avoid the hot steam in the pot. Hit the saute button, and bring the soup to a low simmer.
Pour the flour mixture into the soup, and whisk until fully incorporated. Let the soup simmer for a few minutes until it's thickened some. Hit cancel to stop the pot from cooking.
If you like a chunkier potato soup with a thinner broth, proceed to the next step. If you enjoy a slightly thicker broth with smaller chunks of potato for added texture, use a potato masher and gently smash some of the potatoes.
Add the heavy cream, stirring to evenly combine. Season the soup with additional salt & pepper, if desired.
Ladle the soup into bowls, and serve hot.