Trim excess fat from the 5–6 chicken thighs and pat them dry.
In a bowl, combine 2 teaspoons olive oil, the lemon zest and lemon juice from 1 lemon, 2 teaspoons minced garlic, 1/2 teaspoon salt, 1/4 teaspoon black pepper, and 1/2 teaspoon Italian seasoning; rub the mixture all over the chicken thighs.
Set the Instant Pot to Sauté (Normal) and heat 1 tablespoon olive oil until shimmering.
Brown the chicken thighs 1–2 minutes per side until golden; they will not be fully cooked through. Transfer the browned chicken to a plate.
Pour half of the 1 cup chicken stock into the pot and scrape any browned bits from the bottom with a spatula; then add the remaining stock and any reserved lemon juice.
Place the trivet in the Instant Pot and arrange the browned chicken thighs on the trivet.
Close the lid, set the valve to sealing, select Manual/Pressure Cook on HIGH pressure, and cook for 7 minutes.
When the cooking cycle finishes, press Cancel and allow a natural pressure release until the pin drops; then open the lid away from your face and remove the chicken to a plate.
To make gravy (optional): mix 2 teaspoons cornstarch with 1 tablespoon water, stir into the liquid left in the pot, and simmer on Sauté until slightly thickened.
Serve the chicken with the pan gravy if desired.