Set Instant Pot to sauté mode, add beef and sear for 2 to 3 minutes per side.
Season with salt and pepper, then add garlic, Worcestershire sauce, thyme, tomato paste and beef broth.
Top beef with potatoes and carrots.
Cover and lock the lid in place. Place the vent to the sealing position and set to manual on high pressure for 40 minutes. When the cook time is done, allow the pressure to naturally release for 15 minutes.
Release remaining pressure and remove the lid. Using a slotted spoon, transfer carrots and potatoes to a serving dish. Transfer pot roast to same dish and garnish with parsley.
If a gravy is desired, set the pot to saute mode and bring cooking liquid to a simmer. Mix a tablespoon of cornstarch with 3 tablespoons of cooking liquid. Add the cornstarch mixture back to the simmering liquid; cook and stir until thickened. Spoon some of the gravy over the pot roast before serving.