It was last November when both Microsoft and Apple blocked iCloud from installing on Windows 10 October 2018 machines due to compatibility and instability issues with both software which causes issues updating or synching with Shared Albums in iCloud. Eventually, Apple released a newer version iCloud version (7.8.1) that fixes the said issue.
In line with Apple’s software being fixed, Microsoft has announced that they will lift the upgrade block mid-February. After which these blocked devices will be offered Windows 10, version 1809 automatically.
With users using the older version of iCloud, Apple or Microsoft wmay send you notifications to update your iCloud to the latest version 7.8.1 before being able to upgrade to Windows 10 version 1809.
If you need the latest version of iCloud, you can download it from here.