Nextcloud is a personal cloud server, you’re not relying on Apple cloud or Google or Dropbox to hold and secure (laughable) your data. If you have a Raspberry Pi at home you can host your own cloud server. There are desktop apps for Windows and Macs and apps for almost ALL mobile operating systems too.
I’ve gone for the personal route because I find the free cloud server really don’t offer enough storage space, and security is a joke for most of them. Plus with the SSL guide you can make sure your is as secure as possible.