Heat the Instant Pot on saute mode. Add the oil to the pot. Season the pork chops on both sides with salt and pepper.
Place the pork chops in a single layer in the pot; you may need to work in batches.
Cook for 3-4 minutes per side or until browned. Remove the chops from the pot.
Melt the butter in the pot. Add the onions and mushrooms and cook for 5-6 minutes or until vegetables are tender. Add the garlic and cook for 30 seconds. Season the vegetables with salt and pepper.
Stir in the thyme leaves and cook for 30 seconds. Pour 1 cup of the broth into the pot and add the pork chops back into the pot.
Close the lid of the pot and turn the vent to the sealing position. Turn the pot to manual high pressure for 5 minutes.
After the cooking time has elapsed, let the pressure release naturally for 10 minutes, then carefully turn the knob to manually release the pressure.
Uncover the pot and place the pork chops on a plate. Turn the pot back to saute mode. Mix the corn starch with the remaining 1/4 cup of chicken broth.
Pour the corn starch mixture into the pot and bring to a simmer. Cook for 1-2 minutes or until gravy has thickened.
Spoon the gravy over the pork chops. Sprinkle with parsley, then serve.