Preheat a 5-quart or larger air fryer to 400°F for 3 minutes. Pierce each potato 6 times with a fork, then rub with olive oil and salt.
Place potatoes directly in the basket with space between them, without foil. Air fry for 25 minutes.
Turn the potatoes and cook for 20 to 25 minutes more until a skewer slides through the center without resistance and the skins are dry and crisp. Add 5 minutes if a center is still firm.
Transfer to plates and rest for 3 minutes. Cut a long slit in each potato, press the ends inward gently and fluff the exposed flesh with a fork.
Add 1 tablespoon butter and half the black pepper to each potato and serve immediately.