Mix the flour, brown sugar, baking powder, salt, cinnamon, and nutmeg together in a large bowl.
Use a fork or pastry blender to cut the butter in until it's crumbly (resembling wet sand) and no longer visible.
Add the diced apple and toss to coat before adding the Greek yogurt. Continue tossing/stirring everything together until a crumbly dough begins to form (a fork works fine for mixing).
Empty the dough onto a flat surface and use your hand to form a ball of dough. Press the dough flat into a rough 6"x4" oval shape about 1/4"-1/2" thick. Don't worry about the perfect size/shape here.
Spray an air fryer basket with nonstick cooking spray before placing the dough in and air frying at 375ºF for 12-14 minutes until golden brown on top.
For the glaze, mix the powdered sugar and water together and pour/brush over the fritter as it comes out of the air fryer.