Mix paprika, salt and pepper in a small bowl. Coat tops (smooth side) of chicken thighs in seasoning mixture.
Add olive oil and 1 tbsp butter to the Instant Pot. Using the display panel select the SAUTE function.
When oil gets hot, brown the chicken on both sides, 3-4 minutes per side. Meat will not be cooked through. Do not crowd the pot–you may have to work in batches. Transfer browned meat to a shallow dish and cover loosely with foil.
Add onion and remaining 2 tbsp butter to the pot and saute until soft, 3-4 minutes. Add garlic and crushed rosemary and cook for 1-2 minutes more.
Add lemon juice and zest to the pot and deglaze by using a wooden spoon to scrape the brown bits from the bottom of the pot.
Put the chicken back into to the pot in one even layer, seasoned side up.
Turn the pot off by selecting CANCEL, then secure the lid, making sure the vent is closed.
Using the display panel select the MANUAL or PRESSURE COOK function*. Use the +/- keys and program the Instant Pot for 7 minutes.
When the time is up, let the pressure naturally release for 5 minutes, then quick-release the remaining pressure.
Serve chicken topped with fresh parsley and lemon slices.
*The MANUAL and PRESSURE COOK buttons are interchangeable.