Apple pushed out iOS 11.4 on May 29 to iPads and iPhones, which included the long-awaited Messages in iCloud feature. The company did not release macOS High Sierra 10.13.5 at the same time, limiting the usefulness of being able to sync messages in the cloud since 10.13.4 is not compatible with Messages in iCloud. But three days later, Apple finally released macOS 10.13.5.
Apple isn’t very consistent when releasing new macOS versions that coordinate with new iOS ones. Sometimes the Mac updates come at the same time, sometimes it’s a few hours later, sometimes it’s days later. For some examples, iOS 11.0 was released six days before macOS 10.13, the iOS 11.1 and macOS 10.13.1 updates were released at the same time, and macOS 10.13.4 came out about six hours after iOS 11.3.
The biggest feature that users have been waiting for since September 2017, aside from AirPlay 2, is Messages in iCloud, which stores all texts and iMessages in iCloud and syncs between iPads, iPhones, iPod touches, and Macs. So it seems odd that Apple waited so long to release macOS High Sierra 10.13.5 when users wouldn’t be able to utilize Messages in iCloud to its fullest without its Mac counterpart.
Oddly enough, Apple did push out an update for iTunes 12.7.5 shortly after iOS 11.4, which includes minor app and performance improvements.
To make this point clearer, if you only have one iOS device and a Mac or two, Messages in iCloud wouldn’t help you sync conversations across your devices without both iOS 11.4 and macOS 10.13.5. This has been a huge issue for a long time when it comes to permanently deleting messages since deleting them on an iPhone will not delete them from the Messages app in macOS.
https://ios.gadgethacks.com/news/messages-icloud-finally-available-for-macs-not-just-ios-devices-0185000/