Preheat the oven to 180°C (350°F) and line a muffin tin with paper liners or lightly grease it.
In a large bowl, mix the flour, baking powder, baking soda, salt, and cinnamon.
In another bowl, combine granulated sugar, brown sugar, melted butter, eggs, vanilla extract, and milk until smooth.
Gradually add the dry ingredients to the wet ingredients, stirring gently until just combined without overmixing.
Fold in the diced apples carefully.
In a small bowl, mix the flour, brown sugar, and cinnamon for the crumb topping.
Add the softened butter and work it in with a fork or your fingers until the mixture resembles coarse crumbs.
Spoon the muffin batter into the prepared cups, filling each about three-quarters full.
Sprinkle the crumb topping evenly over each muffin.
Bake in the preheated oven for 18-22 minutes or until a toothpick inserted in the center comes out clean.
Allow the muffins to cool in the pan for a few minutes before transferring them to a wire rack to cool completely.