Turn on Instant Pot to SAUTE mode, once hot add the butter. Saute onion and celery until tender, about 5 minutes.
In a large bow, toss the bread, herbes de Provence, salt, pepper, garlic powder, and celery salt. Turn OFF Instant Pot. Pour the butter and vegetable mixture over top, toss to combine.
Return mixture to the 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.
Toss and serve with fresh parsley, OR to get extra crisp, transfer to a baking sheet and broil for 5 minutes.