Select the SAUTE setting on the Instant Pot and heat the oil. Then, melt the butter.
Season the chicken with salt and pepper. Cook the first side for 2-3 minutes until golden, adjusting the heat if it browns too quickly. Flip and cook for an additional 2 minutes.
Add minced garlic to the pot and cook for about 30 seconds, or until fragrant.
Pour in chicken or vegetable stock and deglaze the pot, scraping any stuck bits from the bottom. These flavorful bits will enhance the cream sauce and help avoid the BURN message.
Season with Italian seasoning, salt, pepper, and chili flakes.
Secure the lid, set the vent to SEALING, and select the PRESSURE COOK or MANUAL setting. Set the cooking time for 5 minutes at high pressure (or 8 minutes for bone-in chicken thighs). The Instant Pot will take about 6-7 minutes to come to pressure and start cooking. When the cooking program ends, perform a quick release of the steam.
Carefully open the lid, remove the chicken from the pot, and set it aside on a plate.
Switch back to the SAUTE setting. Stir in the heavy cream and freshly grated Parmesan cheese.
Add chopped sun-dried tomatoes and spinach leaves to the pot. Turn off the SAUTE setting and allow the spinach to wilt.
Return the chicken to the pot and spoon the cream sauce over it.
Serve over buttered pasta or rice, garnished with extra grated Parmesan cheese.