Pat your pot roast dry, spread a very thin layer of mustard on it, and season well with salt, pepper, garlic powder, and smoked paprika on all sides. If the roast is not the same thickness all the way through or falling apart, tie it with butcher's twine.
Start Sauté mode and add the 2 tablespoons of olive oil.
When your Instant Pot and olive oil are hot, sear your roast on all sides, about 3-4 minutes per side until you get a nice browning on all sides.
Peel and cut your onions into wedges.
Remove your roast to a plate and add in 1 tablespoons of olive oil. Add in the onion wedges and sauté them, removing the brown bits from the bottom of the pan.
In a measuring cup, add the gravy ingredients and mix well. Add the gravy to the pot and deglaze well.
Place your veggies in the Instant Pot along with the onion and wine mixture. Add in the roast, nestling it between the veggies, pour your sauce ingredients over them, and cook on high pressure for 60 minutes.
Wash and chop your potatoes, carrots, and celery into pieces that are slightly larger than bite sized.
Let the pressure release and open your pot. Remove the veggies and the meat and shred it.
For a thicker gravy, make a cornstarch slurry from 2 tablespoons of cornstarch and 4 tablespoons of water and mix it with the cooking liquid. Boil on sauté mode until the cornstarch is cooked and the gravy's consistency is to your liking.
Pour the gravy over the meat and veggies on a serving plater. Garnish with some chopped parsley. Serve and enjoy.