I updated all my idevices last night and enabled Messages in iCloud on my iPhone 8 and waited for it to upload. I then went to my Mac and applied all updates (only update was for itunes). But there's no option in Messages > Preferences. The Apple support docs indicate this should be an option. Beta testers with 10.13.5 seem to have it. I have 10.13.4 but no option to update to 10.13.5. I've checked in iCloud.com as well, but there's no options there to manage which devices can play with Messages in iCloud. Am I missing something? I'm stuck on the fact that Apple has a document saying how to use it, but no reference to a forthcoming update. https://support.apple.com/en-us/HT208532 Interestingly, I have the same issue with my Apple Watch. I updated it too, but there's no options in the Watch itself, the Apple Watch app, or elsewhere on my phone, etc that allow me to control Messages in iCloud on the watch. But I know for sure that messages deleted on the phone are not deleting on the watch and vice versa.