Preheat the air fryer to 350°F (175°C).
In a mixing bowl, combine the flour, granulated sugar, baking powder, salt, and ground cinnamon. Mix well.
In a separate bowl, whisk together the melted butter, milk, and vanilla extract until combined.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix; the dough should be slightly sticky.
Turn the dough out onto a floured surface. Roll it out to about ½ inch thickness.
Use a biscuit or cookie cutter to cut out the donut biscuit shapes. Place them on a lightly greased air fryer basket, leaving space between each.
Air fry the donut biscuits in batches for 8-10 minutes or until golden brown and cooked through.
While the biscuits are cooking, prepare the glaze. In a small saucepan, whisk together the powdered sugar, 2 tablespoons of milk, and ½ teaspoon of vanilla extract until smooth. Set aside.
Once the donut biscuits are done, remove them from the air fryer and let them cool on a cooling rack for a few minutes.
Dip each warm donut biscuit in the glaze, covering the top and allowing the excess to drip off. Place back on a cooling rack to set.