Season beef with salt and pepper.
Open Instant Pot. Select sauté and add in oil.
Sear outside of pot roast.
Prepare remaining ingredients, while beef is searing.
Cancel to stop saute, remove pot roast and add in garlic, onions, mushrooms, carrot and celery.
Place pot roast on top, add water and close the Instant Pot.
Select high pressure cooking for 40 minutes.
When done, let pressure release naturally, then remove pot roast and vegetables. Let the pot roast rest at least 10 minutes before cutting.
To make gravy, select sauté.
Combine corn starch and water to make slurry.
Add slurry to liquid in instant pot and stir until gravy thickens and is has started to heat up (bubbling). Then select cancel and gravy is done.
Serve pot roast sliced with gravy and enjoy.