Cut the croissants in half lengthwise.
In a shallow bowl, whisk together the eggs, milk, vanilla extract, ground cinnamon, and a bit of granulated sugar until well combined.
Gently dip each half of the croissants into the custard mixture. Be careful not to soak them too long to avoid them getting soggy.
Preheat your air fryer to 350°F (175°C).
Lightly grease the air fryer basket with butter to prevent sticking.
Place the dipped croissants in the air fryer basket in a single layer. Depending on the size of your air fryer, you may need to do this in batches.
Cook for about 4-5 minutes, then carefully flip each croissant and continue cooking for another 3-4 minutes or until they are golden brown and crispy on the outside.
Serve the croissant French toast hot. You can top them with fresh berries, a dollop of whipped cream, a sprinkle of powdered sugar, or a drizzle of maple syrup for added flavor.