Place seasoned potatoes in the air fryer at 400°F for 15-20 minutes until crispy. Shake halfway through for even cooking.
Heat a cast-iron skillet over medium-high heat with the remaining olive oil. Sear filets for 1 minute per side, then remove from the pan.
Lower heat to medium-low and melt 4 tbsp butter in the skillet. Add thyme and smashed garlic. Return steaks to the pan and sear for 5 minutes, flipping every minute while spooning melted butter over them.
Remove filets from the pan and let them rest for at least 5 minutes.
Increase heat to medium-high and cook the broccolini in the same pan for 2-3 minutes per side until slightly charred.
Arrange crispy potatoes, broccolini, and juicy filet mignon on a plate. Enjoy!