Set Instant Pot to Saute - Normal mode. When it reads "Hot" add the oil and wait for the oil to heat up.
Brown the meat in batches. If needed cut the chuck roast in two, so it fits in the pot. Cook each piece on EACH side for full 5 minutes without turning.
If needed, add a bit more oil to the pot when searing the rest of the pieces.
Remove the seared pieces on a plate and cover with foil to keep them warm.
Once all the beef has been browned and set aside its time to deglaze the pot.
Add the 1/2 cup of water to the pot and using a wooden spoon scrape the bits and pieces that stuck to the bottom and sides of the pot until its cleared.
Add onion and minced garlic and cook for 1 minute, stirring occasionally.
Add the beef broth, Pepperoncini juice and Worcestershire sauce.
Add the salt, pepper, red pepper flakes, Ranch dressing dry mix and Au Jus mix. Stir to combine.
Turn off the sauté mode.
Add the beef in layers, and add sliced butter and garlic cloves between each layer.
Add the Pepperoncinis to the pot as well as bay leaves.
Close the lid and seal the valve. Cook for 70 minutes on High Pressure. Once the Instant Pot beeps, do a 15 Minute Natural Pressure Release. Release manually the remaining pressure.
Open the lid and turn the Instant Pot to Sauté mode.
If you want the gravy to be thicker, mix cornstarch and water in a small bowl until fully combined.
Add the mixture to the pot and gently stir. Let it simmer for 2-3 minutes. If you want to thicken it even more, add another round of cornstarch slurry. The sauce will thicken more as it cools off as well.
Discard the bay leaves and serve the roast with mashed or baked potatoes. Garnish with extra Pepperoncinis and chopped parsley.