Cut the beef chuck roast in half.
Sprinkle the salt, pepper and 1 teaspoon dried thyme (if not using fresh thyme) on all sides of the beef. (If using fresh thyme sprigs you will add them later.)
Heat the olive oil in the Instant Pot using the saute setting until hot.
Place the seasoned beef in the pot and brown on both sides, about 4 minutes per side. Do not move the beef until you are ready to turn it; once it has seared it should easily release from the bottom of the pot. After browning the beef on both sides transfer it to a clean plate.
With the Instant Pot still on saute mode, add the onion to the pot. Cook until softened and lightly browned, stirring often and scraping up any browned bits from the bottom of the pot, about 4 minutes. Stir in the garlic and press cancel to turn off the Instant Pot.
Add the tomato paste, Worcestershire sauce and beef broth. Stir and scrape up any browned bits from the bottom of the pot.
Place the beef back in the pot. If using fresh thyme sprigs add them now.
Close the Instant Pot lid and turn the steam release valve to the sealing position. Cook on Manual/Pressure Cook, high pressure, for 60 minutes. When the cook time ends, allow the pressure to release naturally for 10 minutes and then quick release any remaining pressure by turning the valve to the venting position.
Open the Instant Pot and add the carrots and potatoes on top of the beef. Close the lid and pressure cook for 10 minutes more on high pressure using the Manual/Pressure Cook function. When the cook time ends allow the pressure to release naturally for 10 minutes.
Remove the beef and vegetables from the Instant Pot. Discard the thyme stems. Use two forks to shred the roast into chunks.
Thicken the juices in the Instant Pot (optional): Turn the Instant Pot on saute mode. Stir together 2 tablespoons cornstarch and 2 tablespoons water in a small bowl and pour into the liquid in the pot. Cook, stirring occasionally, until gravy has thickened slightly.
Serve pot roast with the gravy.