On the Instant Pot choose the SAUTE setting. Heat the oil and melt the butter.
Season the chicken with salt and pepper, and cook the first side for 2-3 minutes until golden (adjust heat if browning too fast), then flip and cook for 2 more minutes.
Add minced garlic to the pot, and cook for 30 seconds or until fragrant.
Add chicken/vegetable stock and deglaze the pot by removing any bits stuck to the bottom of the pot, these bits contain a lot of flavor that will enrich the cream sauce. This step is also important to avoid getting the BURN message.
Season with Italian seasoning, salt, pepper, and chili flakes.
Secure the lid and set the vent to SEALING. Select the PRESSURE COOK/MANUAL setting and set the cooking time for 5 minutes at high pressure/8 minutes if using bone-in chicken thighs. The Instant Pot will take around 6-7 minutes to come to pressure and start cooking. When the cooking program ends, quickly release the steam.
Carefully remove the lid, take the chicken out of the pot onto a plate and set aside.
Choose the SAUTE setting, stir in the heavy cream and the freshly grated parmesan.
Add chopped sundried tomatoes, and spinach leaves to the pot. Switch off the SAUTE setting, and allow the spinach leaves to wilt.
Put the chicken back in, and spoon the cream sauce over it. Serve over buttered pasta or rice with extra grated parmesan cheese.