Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper and set aside.
Slice the bananas into 1-inch (2 to 3-cm) pieces and spread them on the prepared baking sheet.
Sprinkle the bananas with the cinnamon. Bake for 30 minutes, turning once halfway through, until the bananas are brown and soft. Remove from the oven and let cool completely, 30 to 45 minutes.
Combine the bananas, coconut milk, almond milk, and vanilla in a blender and blend until smooth. Taste and add more cinnamon or a splash of sweetener, if desired. Add the cacao nibs and stir with a spoon.
With an ice cream maker:
Pour the mixture into an ice cream maker and prepare according to the manufacturer’s instructions. Serve immediately or transfer to a freezer-safe container, cover, and freeze until ready to serve. Let the ice cream thaw for 10 to 15 minutes. Scoop ice cream into bowls, drizzle with maple syrup, and serve.
Without an ice cream maker:
Pour the ice cream mixture into a freezer-safe bowl and freeze for about 3 hours, mixing well every 30 minutes. Scoop into bowls, drizzle with maple syrup, and enjoy!