Hi,
I’m having same issue on iOS 17.0.3 (latest version available) on new iPad Pro setup Sunday and yesterday - used nearby detected iPhone 14 Plus (running iOS 16.7 at the time) to configure my iPad Pro setup using same Apple ID.
Both iPhone 14 (now on iOS 17.0.3 to link to new Apple Watch last night) and current iPad Air 2 (on iOS 15.7.9 = latest version), all on same Apple ID as iPad Pro, have iCloud sync and backup enabled.
The iPad Pro (on iOS 17.0.3 as updated from factory default version yesterday) shows an unable to sync with iCloud warning in Settings, and refuses to re-establish sync with same unable to connect error: “An Unknown error occurred. Please try again later.” through iCloud Settings on the iPad Pro.
I’ve checked the guidance in the links in above response and issue has not been resolved.
Any further ideas on resolving this issue greatly appreciated!
Best
GG