See this Apple page for details
"Interestingly, Microsoft says the new iCloud app is "powered by the same Windows technology that also powers OneDrive's Files On-Demand feature"—an unexpected technical and corporate partnership. But it shouldn't be too surprising at this point; despite the storied history and rivalries of the 1980s and '90s (as well as competition in areas like, yes, cloud services), Microsoft and Apple have largely played together nicely in recent years.
Apple's iCloud is a full-featured service for storing files and photos, syncing contacts, and other things, as long as you're working solo and not looking to collaborate. (Dropbox, Google Drive, and other competitors offer much more robust features for teams by far.) But iCloud flies under the radar for a lot of people. Its cross-platform support has been mediocre, which doesn't help, so this new version is a welcome update for users who are dependent on the service, provided it actually addresses users' complaints."Apple’s iCloud has been a poor experience in Windows, but a new update seeks to fix that | Ars Technica