Set the Instant Pot on SAUTE function & keep it on NORMAL heat setting. Add 2 tbsp butter + 2 tbsp oil and saute the chicken until lightly golden around the edges. Set them aside.
In the same pot add the rest of the butter & saute the garlic for 30 seconds.
Add the onion and saute until the onion begins to become limp. Immediately reduce the heat to LOW settings,
Now, add the flour and stir briskly. Saute for about 1 min. Pour the white wine and mix everything briskly with the help of your spatula scraping the bottom of the pot.
Now, add the chicken stock bit by bit in 2-3 batches. Keep stirring everything in the pot every time to add the stock and keep mixing briskly so that the roux is uniformly incorporated without any lumps.
Add all the seasonings mentioned above in the "Seasonings" section and mix well. Also de-glaze the pot very well with the help of your spatula scraping the sides and the bottom of the pot. This will prevent the BURN error. There should not be any food particles stuck at the bottom of the pot.
CANCEL the SAUTE function and add the diced mushrooms. Now add the egg noodles and layer them in a single layer. DO NOT mix or stir anything in the pot. Gently press down the egg noodles with the help of your spatula.
Now, layer the sauteed chicken on top of the noodles in a single layer. DO NOT stir or mix anything in the pot.
Cover the lid. SEAL the valve and PRESSURE COOK on HIGH for 2 minutes.
Once the pressure cooking cycle is over do a quick pressure release (QPR) manually by moving the valve from the SEALING to the VENTING position. Once the metal pin drops open the Instant Pot.
Turn off the Instant Pot immediately.
Now add the sour cream and cream cheese both at room temperature and mix gently with the cooked noodles. If you feel the sauce is thicker you can add an additional 1/3 cup water or stock (not mentioned in the ingredients above).
Remove the steel insert immediately from the base of the Instant Pot and keep it on the counter top. This will prevent the delicate egg noodles from getting over-cooked with the trapped heat from the base of the Instant Pot.
Garnish with chopped parsley and serve immediately for best noodle texture. Enjoy!