Isn't it still unsupported to upgrade from one stable Debian version to another? I mean I know you can hack your way around it, just change the apt repos to point at the new release, run apt update, upgrade and dist-upgrade, and hope that not too much stuff breaks. But the nice thing about Ubuntu, especially for less technical people, is that the system will just prompt you to update when it's time, and the upgrade process is supported and well-tested.