Preheat the oven to 375°F. Line a standard 12-well muffin pan with paper liners or coat the wells with cooking spray.

Stir together the melted butter, flour, granulated sugar, brown sugar, ground cinnamon, and kosher salt in a medium bowl with a fork until evenly moistened and a variety of crumb sizes form. Do not mix into a paste of uniform consistency.

Whisk together the all-purpose flour, baking powder, and ground cinnamon in a medium bowl.

In a large bowl, whisk together the melted butter, granulated sugar, neutral oil, and kosher salt. Whisk in the milk, eggs, and vanilla extract until combined.

Fold in the flour mixture and the peeled and diced apple with a flexible spatula until just combined. Do not overmix.

Divide the batter between the muffin wells (about generous ¼ cup per well). Break up the topping and sprinkle it evenly over the batter (about 2 tablespoons per well).

Bake until the muffins are golden-brown and a toothpick inserted into the center of a muffin comes out clean, about 22 to 25 minutes. Let cool for 5 minutes. Transfer the muffins to a wire rack and let cool completely.

Whisk together the powdered sugar and milk in a small bowl until smooth. If the glaze is too thick to drizzle, whisk in more milk a few drops at a time as needed. Drizzle the glaze evenly over the muffins with a small spoon and let sit until set, about 15 minutes.