Leaving coconut cake out overnight can be a bit iffy, especially if it has any kind of dairy in the frosting or filling. If it’s just a plain coconut cake without any perishable ingredients, it might be okay for one night. But to be on the safe side, I'd recommend covering it and putting it in the fridge.
Leaving coconut cake out overnight is not recommended because it can spoil and pose food safety risks. Store it in the fridge in an airtight container. Bake ahead for brunch, but let it come to room temp before serving. Enjoy!