http://j4dhkkxfcg2wdksyueimyoykwhirscttska5wtag6hvhqoqfphqd7yad.onion/ru/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).