Prepare the dry ingredients: In a large mixing bowl, whisk together the flour, sugar, baking powder, salt, and cinnamon until well combined.

Mix the wet ingredients: In a separate bowl, combine the milk, eggs, melted butter, and vanilla extract. Whisk until smooth.

Combine wet and dry ingredients: Gently fold the wet mixture into the dry ingredients until just combined, then fold in the diced apples.

Preheat the waffle iron: Preheat your waffle iron according to the manufacturer's instructions and lightly grease it.

Cook the waffle donuts: Scoop the batter into the waffle iron and cook for about 5-7 minutes until golden brown.

Cool the waffles: Remove the waffles from the iron and let them cool on a wire rack.

Shape the donuts: Using a donut cutter, cut shapes from the cooled waffles.

Heat the oil for frying: Heat vegetable oil in a deep skillet to 350°F (175°C).

Fry the donuts: Carefully lower the shaped waffles into the hot oil for about 2-3 minutes on each side until golden brown.

Drain excess oil: Remove the fried donuts from the oil and place them on paper towels.

Prepare the glaze: Whisk together powdered sugar, milk, and vanilla extract until smooth.

Glaze and serve: Dip each cooled donut into the glaze and place it on a wire rack to set.