I used iCloud Drive for a while since it was a two-fer with iPhone backups and end-to-end encryption.
But for some reason the Windows Store client is garbage. I’ve done the reinstall, etc. dance but it keeps hanging while attempting to sync and ballooning logs to hundreds of MB.
So I have no cloud storage. I instead just plug in my phone to iTunes for it’s periodic local backup and drag-and-drop whatever files I want to have on my phone then.