Preheat the oven to 350°F and line a 12-cup muffin pan with parchment paper cups.
In a medium bowl, whisk together the flour, baking powder, cinnamon, and salt.
In a large bowl, combine the sugars, Greek yogurt, oil, eggs, and vanilla. Whisk until smooth.
Add the dry mixture on top of the wet mixture and whisk until just combined, with no flour streaks remaining. Gently fold in the diced apples. Rest the batter for 10 minutes
Meanwhile, make the crumb topping. Melt the butter in a small bowl. Add flour, brown sugar, and cinnamon and mix until crumbly.
Divide the muffin batter evenly into the prepared pan, then sprinkle the crumb topping evenly over each.
Bake for 18–20 minutes, or until a toothpick inserted in the center comes out clean.
Allow muffins to cool in the pan for about 5 minutes, then transfer to a wire rack to cool completely.