Whisk flour, milk, egg whites, oil, and salt together in a large bowl until smooth.

Lightly coat a skillet with cooking spray and place over medium heat. Pour 1/4 cup batter into the skillet and immediately rotate the skillet in a circular motion to spread batter out to edges in a thin layer. Cook until the bottom is light brown, about 2 minutes.

Flip crêpe; place 2 tablespoons mixed berries in center of crêpe and cook 2 minutes more. Fold crêpe in half; transfer to a serving plate using a spatula. Dust with confectioners’ sugar; serve. Repeat with remaining batter, berries, and confectioners’ sugar.