Add butter to the Instant Pot. Using the display panel select the SAUTE function.
When butter is melted, add onion to the pot and saute until soft, 3-4 minutes. Add garlic and cook for 1-2 minutes more.
Add broth to the pot and deglaze by using a wooden spoon to scrape the brown bits from the bottom of the pot.
Add the chicken to the pot, then secure the lid, making sure the vent is closed.
Using the display panel select the MANUAL function*. Use the +/- keys and program the Instant Pot for 5 minutes.
When the time is up, let the pressure naturally release for 5 minutes, then quick-release the remaining pressure.
Remove the chicken to a serving platter.
Whisk the flour into the half and half until smooth. Stir into the pot along with the parmesan cheese. Cook and stir until thickened, about 3-4 minutes, returning to SAUTE mode as needed.
Stir in the spinach and adjust seasonings.
Serve sauce over the chicken, alongside noodles, zucchini zoodles, rice or vegetables.
Notes
*The MANUAL and PRESSURE COOK buttons are interchangeable.