http://j4dhkkrfv66no3miwc7dv22cytk4rcjlsv6yqsjxgcnkswxqlbjuh2qd.onion/en/privacy_policy
Excluding the files, everything else (calendars, contacts, news, tasks, bookmarks, etc.) is stored unencrypted in a database, unless an application provides external encryption (none so far). This is a limitation of the software we are utilizing for this service (Nextcloud).