Place 5 tablespoons of butter, garlic powder, onion powder, smoked paprika, thyme, salt and pepper in a bowl. Stir until combined.
Loosen the skin of the chicken. Spread half of the butter mixture underneath the skin of the chicken, and spread the rest all over the outside of the chicken.
Place the lemon and onion wedges into the cavity of the chicken.
Pour the chicken broth into the bottom of an Instant Pot.
Place a trivet in the pot. Place the chicken, legs up, on the trivet.
Close the lid of the pot and turn the vent to the sealing position.
Set the pot to manual high pressure for 24 minutes.
After the cook time has ended, let the pressure release naturally for 15 minutes, then manually release the rest of the pressure.
Carefully transfer the chicken to a sheet pan. Preheat the broiler.
Broil the chicken for about 4 minutes or until skin is browned and crispy.
Set the pot to the Saute function and bring the remaining liquid to a simmer. Whisk together the corn starch with 3 tablespoons cold water.
After the liquid has come to a simmer, whisk in the corn starch mixture. Bring to a boil, and cook for 1-2 minutes or until gravy has thickened. Whisk in the remaining tablespoon of butter. Season with salt and pepper to taste.
Let the chicken rest for 5 minutes, then slice and serve with the gravy. Garnish with fresh herbs if desired.