What is your block element structure for the carousel?

The format needs to be {<alias prefix>: <contents>} so if the alias of the data you're trying to render is carousel then it would be {umbValue: carousel}.

The fact that {umbValue: Carousel} returns nothing suggests that Carousel is not the alias of a property. It's not a valid alias - it should be camelCase.

= is shorthand for umbValue so would be {=<property alias>} e.g. {=carousel}.