Preheat your air fryer to 375°F.

In a large mixing bowl, whisk together flour, sugar, baking powder, baking soda, and salt.

Add the cubed butter and stir. Using a pastry blender, cut the butter into the flour mixture until it resembles small broken-up peas. Add the buttermilk and stir until evenly distributed throughout the batter. Very gently, knead the dough, just until it comes together in a ball.

Transfer to a lightly floured work surface and pat into a rectangle. Fold the sides of the dough over and onto itself, just as if you were folding a piece of paper to place in an envelope. Dust with flour if needed and roll out until the dough is about a ¼" thick.

Use a 2 ½-3" round cookie or biscuit cutter, cut out as many circles as you can, and set aside. Bring the dough scraps back together once more and repeat. For donut holes, use a ¾-1" round cutter to cut holes from the center of the dough rounds. Roll the holes into little balls and set aside.

Place the donuts in the air fryer in a single in your air fryer and cook for 4-5 minutes. You will likely need to cook the donuts in 4 separate batches. Add the donut holes to the air fryer and cook for 3-4 minutes, shaking the basket about halfway through the cook time.

Set a rack on top of a work surface lined with wax or parchment paper.

Combine the powdered sugar, milk, and vanilla in a shallow bowl and stir until smooth.

Dip both sides of the donut in the glaze and transfer to the rack and allow to set, about 10-15 minutes.

Add the melted butter to one shallow bowl and in another, combine the granulated sugar, cinnamon, and salt.

Submerge the donut in the butter, allowing any excess to drip off, then coat thoroughly in the cinnamon-sugar mixture.