Preheat the oven to 300° F. Line a large baking sheet with parchment paper.
Combine the Rice Chex with the pretzels and chopped almonds in a large, heatproof bowl. Add in the melted butter and cinnamon and stir to coat everything in the butter.
Spread the mixture evenly on the prepared baking sheet. (Keep the large bowl aside.) Bake the mixture for a total of 30 minutes, stirring every 10 minutes.
Remove the sheet from the oven and transfer the mixture back to the large bowl. Add in the semisweet and white chocolate chips and the rainbow sprinkles. Stir to combine everything together - the chocolates will become melty and bring the snack mix together into tasty clumps. Allow the mixture to cool to room temperature before transferring it to a serving bowl.
The snack mix can be stored in a sealed container for up to 5 days.