Mix all herb butter ingredients in a small bowl. If using whole turkey, butterfly the breast and stuff with herb butter. If using a roast, cover herb butter over all turkey pieces. Tie the breast together using kitchen twine. Rub remaining 4 tbsp butter over the skin.
Place carrots, celery, parsley, garlic, thyme, and chicken broth in the Instant Pot. Layer the cooking rack on top of the vegetables. Salt the stuffed turkey breast, and place on the rack skin side up.
Pressure cook on HIGH for 6 min per pound, setting the timer for a 10 minute natural release. BROIL at 400F for 20 minutes until the skin is golden and crispy. Turkey breast should read at least 165 on a meat thermometer.
Remove the turkey breast and rest for 15-20 minutes, tenting with aluminum foil to keep warm.
Strain the liquid and discard any vegetables or herbs. Keep leftover broth in a separate bowl.
While the turkey is resting, make the gravy. Turn the SAUTE function on Level 3 for 10 minutes. Melt the butter for the gravy and whisk in the flour. Toast the flour and butter for 1-2 minutes, or until fragrant. Pour in reserved broth and whisk vigorously to eliminate all lumps. Bring to a boil and cook for 3-5 minutes , until thickened.Add salt to taste.