Remove roast from refrigerator and allow to rest at room temperature. Do not cut netting or string.
Sprinkle entire breast, on all sides with salt, pepper, and poultry seasoning.
Set Instant Pot to SAUTE setting and add olive oil and butter. Once butter is melted and the oil is hot, brown turkey breast on all sides (about 2-3 minutes per side). Remove from the Instant Pot and press CANCEL.
Add broth and scrape any bits from the bottom of the pot. Add onion, celery, and 3 Tablespoons of fresh herbs (reserving 1 Tablespoon for garnish).
Add trivet and place turkey breast (skin side up if there is skin).
Set the Instant Pot to HIGH PRESSURE for 22 minutes. Allow natural release for 10 minutes, then quick release. The internal temperature should have reached 160˚F* using a digital thermometer.
Remove roast from the Instant Pot and lightly tent with foil. Rest for 10-15 minutes, until roast reaches 165˚F.
Carefully remove string from the turkey breast (kitchen scissors work well for this).
Optional: place turkey breast, skin side up if there is skin, into a roasting pan and broil for 3-4 minutes to crisp the skin and brown the turkey.
Slice and garnish with reserved Tablespoon of herbs if desired.
Gravy
Remove onions and celery from the Instant Pot. Strain liquid if desired*. Set Instant Pot to SAUTE and bring liquid to a boil.
Combine cornstarch and water to create a slurry.
Slowly add the slurry to the hot liquid and boil for 2 minutes, stirring continuously. Add ½ Tablespoon of fresh herbs if using. Add additional fresh herbs, salt and pepper to taste.
Notes
*If the turkey breast has not reached 160˚F, either return it to the Instant Pot and set it for 5-10 more minutes (adjust based on how close it is to temperature). Or if you plan to brown the breast before serving, pop it in the oven for about 10-15 minutes (at 350˚F) before broiling. It's recommended to use the Instant Pot if not browning the breast. But if the plan is to brown the turkey breast, the oven is a good option to bring it to temperature.
**For a more clear gravy, strain the liquid and add it back to the Instant Pot.
Refrigerate leftovers in a covered container up to 5 days.
Leftover turkey can be frozen in zippered bags for up to 3 months.