Turn on the Instant Pot to SAUTE mode, and once hot, add the butter. Saute the onion and celery until tender, about 5 minutes.
Ina large bowl, add the bread, herbs de Provence, salt, pepper, garlic powder, celery salt and broth and mix together. Turn OFF Instant Pot. Pour the butter and vegetable mixture over top of the bread mixture and toss to combine.
Scrape any crispy bits out of the instant pot and wash out the instant pot.
Place the trivet into the Instant Pot and pour 1 cup of water into the bottom. The water will be under the trivet.
Using two pieces of foil, create a bowl on top of the trivet inside the Instant Pot, ensuring that the stuffing won't leak out the bottom.
Add the bread mixture to the foil bowl you created inside your Instant Pot. Close lid and lock, turn leaver to seal position. Turn ON to MANUAL mode with HIGH pressure selected for 13 minutes. Let the pressure release naturally. This typically takes 15 to 20 minutes.
Using tongs or hot pads, remove the trivet with the foil and transfer to your preferred stuffing dish. Then, toss and serve with fresh parsley, OR to get extra crisp, transfer to a baking sheet, broil for 5 minutes, and enjoy!