Heat oven to 400°F. Line a large baking sheet with parchment and lightly grease it.
Toss the diced apples with lemon juice in a bowl and set aside.
Whisk flour, both sugars, baking powder, cinnamon, nutmeg, and salt in a large bowl.
Whisk milk, eggs, vanilla, and melted butter in a separate bowl until smooth.
Fold the wet mixture into the dry just until combined. Gently fold in the apples.
Scoop 12 heaping spoonfuls onto the sheet, spacing evenly. Lightly flatten the mounds.
Bake until set and golden at the edges, 14–17 minutes. Cool 5 minutes on the pan.
Stir powdered sugar, milk, and vanilla until smooth. Adjust milk for drizzling consistency.
Drizzle glaze over warm fritters. Let it set a few minutes before serving.