Generously season the pork chops on both sides with salt and pepper.
Once the Instant Pot is heated, add in the oil. Sear the pork chops on each side for 1-2 minutes or until fully browned. This may need to be done in batches to not over-crowd the inner pot of the pressure cooker.
Once the pork has been browned, remove the chops from the Instant Pot and place on a plate.
Add in the butter and mushrooms and onions to the Instant Pot and saute for 1-2 minutes. Add in the garlic and saute for 1 minute longer. Turn the Instant Pot OFF.
Pour in the stock and scrape off any browned bits from the bottom of the pressure cooker. Add in the thyme and Worcestershire sauce to the mushroom mixture. Nestle the pork chops back into the Instant Pot.
Place lid on pressure cooker and be sure vent knob is sealed fully. Cook on HIGH pressure for 5 minutes.
Once cook time has elapsed, let pressure release naturally for at least 10 minutes.
Once 10 minutes has passed, release any remaining pressure by hitting the vent knob from sealed to venting (be sure to do this in an open space and stand back from the Instant Pot.)
Remove pork chops and place the pork chops on a clean plate.
Turn the Instant Pot to Saute.
Mix together the cornstarch and water fully and then add that mixture to the inner pot, stirring well. Let cook 1-3 minutes, or until the gravy has thickened up.
Serve the pork chops with the gravy.
Be sure to use 1.5 cups of stock if using an 8 quart Instant Pot.