In a small mixing bowl, combine the shredded cheddar cheese, shredded mozzarella cheese, diced bell peppers, and diced white onion.
Add the eggs, heavy cream, kosher salt, and black pepper. Whisk gently until just combined — do not over-whisk.
Spray ramekins, silicone egg bite molds, or muffin cups thoroughly with non-stick cooking spray, coating the sides as well as the bottoms.
Pour the egg mixture into the molds, filling each about two-thirds full.
Place the molds in the air fryer basket with space between them. Set the temperature to 320°F and cook for 6 to 9 minutes, checking at the 6-minute mark.
The bites are done when the centers are just set and no longer jiggle. Let rest 3 to 5 minutes before releasing from the molds.