Prep the steak: Pat the steak dry with paper towels.
Trim excess fat and cut into 1-inch cubes. Dry meat browns better and helps form that crust.
Season generously: In a bowl, toss the steak bites with olive oil, kosher salt, black pepper, smoked paprika, garlic powder, and red pepper flakes if using. Make sure each piece is coated evenly.
Preheat the air fryer: Set to 400°F (200°C) for 3–5 minutes.
A hot basket helps sear the meat quickly.
Arrange in a single layer: Add the steak bites to the basket without crowding. Work in batches if needed. Overcrowding leads to steaming, not searing.
Air fry: Cook for 5–8 minutes, shaking halfway, until the edges are browned. For medium-rare, aim for an internal temp of 130–135°F (54–57°C).
Add 1–2 minutes for medium.
Make the garlic butter: While the steak cooks, melt butter in a small pan over low heat. Add minced garlic and cook for 30–60 seconds until fragrant (not browned). Stir in parsley and a splash of lemon juice. Remove from heat.
Rest, then toss: Let steak bites rest for 3 minutes in a bowl.
Pour the warm garlic butter over and toss to coat. The resting time helps the juices redistribute.
Serve immediately: Finish with a pinch of flaky salt if you like. Great over rice, with baked potatoes, or alongside a crisp salad.