Preheat the air fryer to 350°F for 3 minutes. Add the olive oil and diced onion to an air fryer–safe pan. Air fry for 4 minutes, stirring once, until softened and lightly golden.
Add the ground beef, chili powder, cumin, and salt to the pan. Air fry at 350°F for 8 minutes, breaking the meat apart with a spatula at the halfway point. Drain excess fat.
Stir in the tomato sauce, black beans, and corn. Air fry at 350°F for 10 to 12 minutes, stirring once, until bubbling and thickened.
Let rest 5 minutes before serving. Top with shredded cheese, sour cream, green onions, or cilantro.
For the cornbread topping: Whisk the corn muffin mix, egg, and milk until just smooth. Spread evenly over the finished chili. Air fry at 375°F for 18 to 20 minutes, until golden and a toothpick comes out clean. Start checking at 15 minutes.