Cut steak into uniform 1.5-inch cubes. Season all sides with kosher salt and place on a wire rack. Refrigerate uncovered for 45 to 60 minutes to dry-brine.
Remove steak from refrigerator and pat every piece thoroughly dry with paper towels. Allow to rest at room temperature for 20 minutes.
Preheat air fryer to 400°F (204°C) for 5 full minutes before cooking.
In a mixing bowl, toss the dried steak cubes with avocado oil, Kinder's Steak Seasoning, minced garlic, and cracked black pepper until evenly coated.
Place steak bites in the preheated air fryer basket in a single layer with small gaps between each piece. Do not overcrowd. Cook in batches if necessary.
Air fry at 400°F (204°C) for 8 to 10 minutes. Open the basket at the 4-minute mark and toss the steak bites to ensure even browning on all sides.
With 2 minutes remaining, add Kerrygold Garlic & Herb Butter to the basket and toss gently to coat all pieces. Allow to finish cooking.
Transfer steak bites to a warm serving plate. Rest for 3 minutes before serving. Finish with flaky sea salt and fresh chopped parsley. Serve immediately