Whisk together creole seasoning, paprika, onion powder, and black pepper; set aside.
Cut beef tenderloin into 1½-inch by 1-inch pieces. Place steak bites, sliced mushrooms, 2½ tbsp oil, and seasoning mix into bowl.
Mix until meat and mushrooms are well coated. Cover bowl and marinate 30 minutes to 1½ hours.
Preheat air fryer to 400°F for 5 minutes. Cook in the air fryer (in 2 batches) at 400°F for 6-10 minutes.
TIP: Beef should be in a single layer with a tiny space between pieces so they don’t steam. Place mushrooms in and around steak. Mushrooms may be cooked seperately at 400°F for 6 minutes.
NOTE: 6 minutes = more rare. 10 minutes = medium-well.
Toss cooked mushrooms and steak pieces in bowl with butter. Sprinkle with more creole seasoning or salt if desired.
Serve with rice, roasted broccoli, noodles, brussels sprouts, couscous, roasted carrots, or a green salad.
