in the iCalendar specification the visibility of an event in shared calendar can be set with the CLASS-parameter. For this parameter, three values are defined in the RFC:

CLASS:PUBLIC --> Event is visible with all details in a shared calendar.
CLASS:CONFIDENTIAL --> event is visible in a shared calendar, but only as "busy".
CLASS:PRIVATE --> event is not visible at all in a shared calendar.

see RFC 5545, Abschnitt 3.8.1.3

It seems, that Business Calendar only implements the values public and private.

Here is what I did:
- Create an event with CLASS:CONFIDENTIAL in Nextcloud.
- Sync the calendar with android (davX5).
- Open Business Calendar --> the event is visible.
- As soon as I try to edit the event, business calendar crashes.
- Event with the values public or private work as intended.

I am not sure, wether this is a bug-report, or a feature-request. :)