Preheat the air fryer. Set your air fryer to 400°F (200°C) for 5 minutes.
A hot basket helps the potatoes crisp and the steak sear.
Prep the potatoes. In a bowl, toss the potatoes with 1 tablespoon olive oil, 1/2 teaspoon salt, 1/4 teaspoon pepper, and 1/2 teaspoon smoked paprika. Coat evenly so every piece roasts well.
Start the potatoes. Add the potatoes to the preheated air fryer basket in a single layer. Cook for 10–12 minutes, shaking the basket halfway.
They should be starting to brown but not fully tender yet.
Season the steak. While the potatoes cook, pat the steak cubes dry with paper towels. Toss with 1 tablespoon olive oil, 1/2 teaspoon salt, 1/4 teaspoon pepper, 1/2 teaspoon smoked paprika, onion powder, and dried thyme. Dry steak browns better, so don’t skip the patting step.
Make the garlic butter. In a small bowl, combine melted butter, minced garlic, and a pinch of red pepper flakes if using.
Set aside.
Add the steak to the basket. When the potatoes have cooked 10–12 minutes, shake to one side or create space, then add the steak cubes in a single layer. Avoid crowding for the best sear.
Air fry to finish. Cook at 400°F for 6–8 minutes more, shaking once halfway. For medium steak, aim for an internal temp of 135°F (57°C).
Add a minute or two for more doneness.
Toss with garlic butter. Immediately transfer steak and potatoes to a bowl. Pour the garlic butter over the top and toss gently to coat. The heat will bloom the garlic and coat everything in flavor.
Finish and serve. Sprinkle with chopped parsley and adjust salt and pepper to taste.
Serve right away with lemon wedges if you like a bright finish.