Turn Instant Pot to saute and add the butter. Once butter is melted, add the onion, celery, and carrots. Cook for 5-7 minutes until veggies are soft. Add the garlic and cook 30 seconds more, until fragrant.
Hit the cancel button on the Instant Pot. Layer the noodles on top of the cooked veggies, then top with the chicken thighs, and pour in the chicken broth, parsley, poultry seasoning, seasoned salt, garlic powder, bay leaf, and pepper to taste. Place the lid on the Instant Pot and turn the vent valve to "sealing." Cook over manual high pressure for 10 minutes.
Allow the Instant Pot to release pressure naturally for 12-15 minutes, then carefully turn the vent valve to release any remaining pressure. Once the pressure is released and the pin has dropped, remove the lid. Remove the chicken thighs to a cutting board and shred. Add the shredded meat back to the pot.
Turn the Instant Pot to saute again. In a small bowl, whisk together the heavy cream and flour to remove lumps, then add the mixture to the Instant Pot. Cook for about 5 more minutes until soup is thickened, stirring frequently. Sprinkle the parmesan cheese over the soup and stir until melted. Turn off the Instant Pot and serve. Enjoy!