The example considerer "cake and ice cream" to be a combined, single thing. Otherwise it would have said "Cake and ice cream are my favorite desserts."
In your examples, do you consider it necessary to have cake and an apple (or two) at the same time? Must you have two cakes for it to be your favorite?
Cake and apples are my favorite desserts. I will be equally happy having cake, or having an apple.
None of your examples work this way.
All of yours require a combination, just like cake-and-ice-cream requires both to be present.