Season the chicken thighs with paprika, oregano, garlic powder, salt, and pepper.
On the Instant Pot, press on SAUTE, add the oil, and melt the butter. Brown the chicken starting skin side down (2-3 minutes), flip and brown it from the other side (2 minutes). When the chicken is golden brown, remove from the pot and set aside. Work in batches if needed.
Add the chicken stock, and deglaze scraping off any stuck brown bits to the bottom of the pot.
Insert a trivet, and put the chicken thighs on the trivet. Slightly overlapping is ok.
Secure the lid and set the vent to SEALING. Select the PRESSURE COOK/MANUAL setting and set the cooking time for 10 minutes at high pressure. The Instant Pot will take around 6-7 minutes to come to pressure and start cooking. When the cooking program ends, allow to naturally release the steam for fall of the bone chicken, or quickly release the steam.
Transfer chicken thighs to a serving plate, and to thicken the sauce to make gravy (optional), set the Instant Pot to SAUTE mode, and add 1 tablespoon of cornstarch mixed with 1 tablespoon of water. Add that to the sauce, and whisk until the sauce thickens. Have a taste and add more salt if needed.
Pour the sauce over the chicken, and garnish with chopped parsley leaves.