Heat the Instant Pot on "SAUTE" mode. Add in 1 tablespoon olive oil. While Instant Pot heats up cut chicken into cutlets. Set to the side. Mix together the all purpose flour, salt, black pepper, and garlic powder into a shallow dish. Coat both sides of the chicken and place in the Instant Pot. Cook for 2 minutes and then flip to sear on the other side for an additional 2 minutes.
Remove the chicken from the Instant Pot.
Add in the remaining 1 tablespoon olive oil, shallot and garlic. Mix for 30 seconds. Then, add in the mushrooms. Cook for 2 minutes.
Deglaze the pan with the Marsala wine. Mix well, add the fresh thyme sprigs and place the chicken on top of the mushroom sauce.
Close the lid making sure the valve is set to "sealing". Turn off the Instant Pot then turn back on for 5 minutes on "MANUAL" mode. Once the chicken is done cooking let rest for 10 minutes and then carefully force the remaining pressure out. Remove the chicken from the pan.
Turn the Instant Pot on to "SAUTE" mode. Let the mushrooms come to a boil. While it starts to warm, mix the cornstarch and water together. Using a silicone spatula begin to mix in the cornstarch slurry into the mushroom gravy.
Mix until it begins to thicken. Turn the Instant Pot off. Add the chicken back to the pot and let sit for 2-3 minutes or until ready to serve dinner.