Would be nice to mention about the enforced return types for @Async annotated functions in the Spring 6 migration guide, see the last lines from my forked wiki here. Could it be an idea to mentioned it?

Functions annotated with @Async must return either a Future or void type. Although the supported return types were documented from the beginning it is now enforced (see 27734) and will throw an exception otherwise.

Comment From: rstoyanchev

Thanks for the suggestion. I've updated the Core Container section.