For example, most parts of iCloud are missing on Android, and their iCloud client for Windows has been broken for months or even years. Its log complains about launching iCloudDrive-AppX.exe while the install directory doesn't contain any executables with a "-AppX.exe" suffix. So no file syncing for me on Windows, I guess.
Having client site updates tied to major macOS/iOS releases is also sometimes causing strange issues if I still want to use older versions of macOS and iOS.
The happy path is only using devices from Apple and always staying on their latest OS release. No idea how attractive this new feature is for people who already use custom domains because they don't want to be tied to a single provider.