Place the stuffing bread in a large bowl. Set aside.
Set the Instant Pot* to sauté.
Add the sausage and cook it, breaking it up, until cooked, about 10 minutes. (If sausage is sticking too much, add ¼ cup of water.)
Transfer the sausage onto a plate.
Add butter into the Instant Pot.
Once butter is melted, add onion and celery and cook for about 5 minutes, stirring occasionally.
Stir in the seasonings and parsley and cook for an additional minute.
Stir in the sausage. Then transfer the mixture into the bowl with stuffing bread. If possible, cover it, so that bread gets warmed up and softens.
Meanwhile, in a medium bowl, whisk together eggs and chicken stock.
Pour it over the bread and sausage mixture and toss to combine.
Replace the stainless steel insert back into the Instant Pot. Place a trivet and pour at least 1 cup of water.
Divide the stuffing into 2 stackable insert pans and place it on the trivet in the Instant Pot. (If you're using these stackable insert pans, then you don't need a special handle, as it comes with one. But if you're using different pan, make a handmade sling using a foil.)
Close the lid, make sure it's in sealing position. Set the Instant Pot to Manual, high pressure, 20 minutes.
Do a quick release, and carefully remove the inserted pans.
Note 1: I used a bag of store-bought plain stuffing bread for this recipe. I also tested preparing the bread cubes myself in the oven (10 minutes at 300°F), but the stuffing was a bit on mushy side.