Peel and core the apples, then slice into 1/2-inch rings. Toss with lemon juice and set aside.
Whisk flour, granulated sugar, baking powder, cinnamon, and salt in a mixing bowl.
Pour in milk and vanilla. Whisk until smooth and pourable; rest the batter 5 minutes.
Heat 1/2 inch of oil in a large skillet over medium to medium-high heat to about 350°F.
Dip apple rings into batter, letting excess drip off so the coating is thin and even.
Fry rings in batches until golden, 2–3 minutes per side. Drain on a rack or paper towels.
Whisk powdered sugar, milk, cinnamon, and vanilla in a small bowl until smooth and glossy.
Drizzle or dip warm rings in the glaze. Let set 3–5 minutes, then serve.