I have a mailcow server with sogo. Here I have calendars from another
user which he shared to me.
The permissions are set so that I can create, modify and delete
[X] This person can add items to my calendar.
[X] This person can delete items from my calendar.
I have synchronized all calendars via CalDAV to my mail client.
Despite the permissions, it is only possible to create appointments. It
is not possible to change or delete appointments. These operations can
be performed only by the owner of the calendar itself, despite the setting.
I suspect a bug here.