Euan WilliamsThis afternoon I tried to back up my iPhone (via Lightning cable) to the 'latest' version of iTunes on High Sierra. However, the all-important tiny iPhone icon to the right of the Music/Films/Audio/Podcasts multichoice dialogue at the top left of the page wasn't there. There is a patch available to regenerate this icon and restore normality.
To get the patch go to this iTunes https://www.apple.com/itunes/download/ page, install as normal and wait for an iPhone Icon alerting you to the patch. The original installer and the patch download and install work concurrently, so be patient.
All is now well here, and with luck Apple will soon issue an updated installer.