Cut the chuck roast into stew-sized chunks. Peel and cut the carrots into chunks. Dice the onion. Chop the baby potatoes into stew-sized chunks.
Turn on the Instant Pot into Saute mode. Add 1 Tbsp of the olive oil and let warm up. Add the beef chunks and cook until all sides are browned. Remove the beef and set aside.
Add the other 1 Tbsp of olive oil. Add the diced onion and saute for 2-3 minutes. Add ½ cup of beef stock to deglaze the pot, making sure to scrape up any bits that are stuck to the bottom of the instant pot.
Add the rest of the beef stock (2 cups) and the tomato sauce to the pot. Stir to combine.
Add the beef, carrots, potatoes, salt, pepper, celery salt, and dried thyme to the pot. Stir to combine.
Place the lid on the Instant Pot, make sure the lid is set to sealing, and set to MANUAL mode. Set the time for 35 minutes. Once Instant Pot is done, let sit for 10 minutes, then Quick Release the steam.
Combine the cornstarch or arrowroot with ½ cup water to make a slurry. Add to the stew and let sit for 3-5 minutes to thicken.
Chop the parsley. Plate the stew, then sprinkle the parsley over the top.