Turn Instant Pot to sauté setting 'more'. When display says HOT add in the oil. Brown the roast on each side for about 4 minutes. Remove the roast and place on a plate.

Add in the onions and baking soda. Toss until the onions start to release moisture and turn yellow (3-4 minutes). Pour in the broth and scrape bottom of pot to ensure nothing is sticking.

Place the roast on top of the onions. Pour garlic, vinegar, Worcestershire sauce, tomato sauce, salt, pepper, thyme, and parsley on top of the roast.

Cover Instant Pot and secure the lid, ensuring the valve is set to sealing. Set the manual/pressure cook button to 60 minutes for a roast that is 2 inches thick. Add 10 minutes for each extra inch of thickness. When time is up, let the pressure release naturally for 15 minutes, then release any remaining pressure by moving valve to venting.

Place the beef on a cutting board. Use a colander or a slotted spoon to separate onions from juices and move them to a platter.

Thicken the juices remaining in the pot with a cornstarch slurry. Turn Instant Pot to sauté setting. In a small bowl, stir together 2-3 Tbsp of cornstarch with 3 Tbsp of water until smooth. Then pour the mixture into the Instant Pot. The cornstarch mixture will thicken up contents of pot quickly. Turn off Instant Pot once gravy is thickened.

Slice or shred beef and serve with the onions and gravy.