today I upgraded from NextCloud 25 to NextCloud 27 and encountered some strange behaviour: When I add NextCloud-CardDAV as second Contact-enabled account on iOS the usual “default account”-option went missing.
The main difference between my old and the new instance seems to be the contact group “Accounts” (in CardDAV URL it is called “z-server-generated–system”), which has not been there on NC 25.
To me it seems like iOS might have trouble with “read-only” address books, like the new “Accounts”-book amongst addressbooks provided by NextCloud.
Unfortunately this “Accounts”-book seems to be default by now and can’t be deleted.
As I read (https://github.com/nextcloud/contacts/issues/1870), earlier versions experienced similar issues when having the “Contacts Interaction” app enabled. I guess this one also created some “read-only”-addressbook, which leads me to the assumption, that iOS might have issues with “read-only”-books in general.
Can anyone confirm on this issue? If so - any ideas what can be done about it?