I'm seeing the same thing and filed FB15150709 - Xcode 16.0 (16A242d) Developer Documentation is not showing Objective-C APIs. Can you help get this fixed?

Some additional context: The 3 key-values which are no more than 30 KB of data each will always perform a successful sync. For the fourth key-value, after setting the data and saving it using NSUbiquitousKeyValueStore and sending a synchronize message, it will always return success, even when device "B" receives an NSUbiquitousKeyValueStoreDidChangeExternallyNotification and the cloud returns an empty value.

Thanks, Quinn. I'll take a look at CloudKit.