Prep the beef. Pat the steak cubes very dry with paper towels.
Dry surfaces brown better.
Season generously. In a bowl, toss steak with salt, pepper, smoked paprika, and half the melted butter. Add soy sauce or Worcestershire. Mix to coat.
Prep the mushrooms. Toss mushrooms with olive oil, a pinch of salt and pepper, and the minced garlic.
Preheat the air fryer. Set to 400°F (200°C) for 3–5 minutes.
A hot basket helps quick browning.
Arrange in the basket. Add mushrooms in an even layer, then scatter steak bites on top. Avoid packing tightly; work in batches if needed.
Air fry. Cook at 400°F for 8–10 minutes, shaking the basket halfway. Aim for medium-rare at 130–135°F internal temp.
Add 1–2 minutes for medium.
Finish with butter. Toss the hot steak and mushrooms with the remaining melted butter. Add chopped parsley or thyme and a light squeeze of lemon if you like.
Rest and serve. Let the steak rest 2–3 minutes so the juices settle. Taste and adjust salt.