Combine the ground beef, breadcrumbs, egg, milk, onion, 1 teaspoon salt, and black pepper in a mixing bowl. Mix until just combined.
Shape the mixture into a loaf that fits your air fryer basket.
Place the meatloaf in the air fryer basket. Cook at 350 degrees for 20 minutes.
Stir the ketchup and brown sugar together in a small bowl to make the sauce.
Brush half the sauce over the meatloaf. Continue cooking for 10 more minutes.
Toss the Brussels sprouts with olive oil and 1/4 teaspoon salt in a bowl.
Add the Brussels sprouts to the air fryer basket around the meatloaf. Cook for 10 to 12 minutes until the sprouts are browned and crisp.
Remove everything from the air fryer. Slice the meatloaf and serve with the remaining sauce on the side.