If you plan to order a new iPhone XS, XS Max or iPhone XR, do not install the iOS 12.1 beta now.
Apple has not yet released a beta version of the operating system for these smartphones. This means that you cannot recover from a backup.
Data backups are not compatible with older versions of iOS. Therefore, you won’t be able to return the saved information.
It is curious that the final build of iOS 12 is also not available for the iPhone XR. But this will probably be fixed by the release of the smartphone on October 19. Buy / use