Turn Instant Pot to saut? 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 they turn yellow, about 3-4 minutes. Pour in the broth and scrape bottom of pot so that nothing is sticking.

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

Cover Instant Pot and secure the lid. Make sure valve is set to sealing. Set the manual/pressure cook button to 60 minutes for a roast that is 2 inches thick. If your roast is thicker, add 10 minutes per extra inch of thickness. After cooking, let the pressure release naturally for 15 minutes and then release any remaining pressure by moving the 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 your Instant Pot to the saut? setting. In a small bowl, stir together 2-3 Tbsp of cornstarch with 3 Tbsp of water until smooth. Pour the mixture into the Instant Pot and stir until the gravy is thickened. Turn off Instant Pot once gravy is thickened.

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