Divide the Chex cereal evenly into two bowls, with 2½ cups in each.
Melt the white almond bark or white chocolate chips in a microwave-safe dish. Add ½ teaspoon shortening to ensure smooth melting. Microwave in 30-second intervals, stirring after each until fully melted and smooth.
Pour the melted white almond bark over the first bowl of Chex cereal. Gently stir to coat the cereal evenly.
Melt the red candy melts in a separate microwave-safe dish, also microwaving in 30-second intervals and stirring after each until melted.
Pour the melted red candy over the second bowl of Chex cereal and mix well to coat every piece.
In two separate gallon-sized ziplock bags, combine ¼ cup powdered sugar and ¼ cup strawberry cake mix.
Add the white almond bark-coated Chex cereal to one bag, seal it tightly, and shake vigorously until coated. Repeat with the red candy-coated Chex cereal in the second bag.
Pour both coated cereals into a large bowl and add the Valentine’s chocolate M&M’s. Toss gently to combine.
Serve immediately or store in an airtight container.