Season the beef well with salt and pepper on both sides. Add the vegetable oil to the Instant Pot, and sear the meat on SAUTE setting for a few minutes, until the surface has browned. Repeat on all sides.
Remove the beef from the Instant Pot, and add diced onions and grated garlic. Saute for a few minutes. If it sticks to the bottom of the pot, you can add a splash of beef stock.
Add the thyme, rosemary, bay leaves, Worcestershire sauce, tomato paste, red wine, and beef stock to the Instant Pot, and gently submerge the chuck roast into the liquid. Seal the pot with a lid, and cook using the MANUAL or PRESSURE COOK setting for 50 minutes on high pressure. Then, do a quick release of the pressure.
Peel the carrots, and cut them into 3-inch chunks. Add these to the Instant Pot, along with the baby potatoes. Try to place them in the liquid on the sides of the roast. Seal the lid on the pot again, and cook with the MANUAL or PRESSURE COOK setting for another 15 minutes on high pressure. Do a quick release to release the pressure after the timer is up.
Remove potatoes and carrots from the Instant Pot. Use two forks to shred the beef in the pot, then remove the beef. Place beef, potatoes and carrots on serving dishes.
Combine the cornstarch with cold water in a small bowl to form a cornstarch slurry. Add this to the liquid in the Instant Pot. Cook the liquid on SAUTE setting for a few minutes while stirring. The liquid will thicken and form a gravy. Use it as is, or strain it to get rid of any chunks of onion or seasoning.
Serve the pot roast immediately with a generous amount of gravy.