How do restore an iOS 12 beta backup to a new iPhone running iOS 11?
I restored an iPhone X from a iOS 12 beta iCloud backup.

Hardware: iPhone X factory reset to iOS 11.

Steps:


Enrolled device into the beta program, installed beta profile and allowed iOS upgrade. After restart pass through all intros to home screen.

Note: Restore from iCloud showed the iOS 12 backups but they are inaccessible.
Go to Settings -> General -> Reset, then tap Erase all content and settings., confirm and restart. This reset the phone again but at the iOS12 level.
Proceed through intros and restore via the now accessible iOS 12 backup.