Hello. 
I have spent some time reading through many posts on Github and this forum to find a solution.
- Nextcloud Server version:
aio v10.1.1 - Operating system and version:
Debian** 12.8.0 "Bookworm
I have a problem with Nextcloud Talk.
It seems that if I allow sharing, all users in the group in question automatically have access to the account address book. But if I prohibit sharing for a group, this group can no longer upload files or photos to Talk groups or chats.
That is very annoying. Because I want all users to be able to upload files in the Talk app, but not to be able to write to other users via the system account address book.
If I prohibit sharing, the address book is no longer accessible, but the option to upload files in Talk is also no longer available.
So I thought that I could somehow restrict access to the account address book and only assign it to certain groups. Unfortunately, I haven’t found anything about this yet.
What I found is this command here to supposedly deactivate the address book. But it didn’t work.
occ config:app:set dav system_addressbook_exposed --value="no"
Talk users should not be able to find each other. They can see each other in group chats, but cannot click on each other to write to each other. 
For me it would be completely fine if the address book function were removed completely. Because I only need to make changes or access the accounts via my admin account.
I don’t know if anyone knows a way to allow uploads in Talk without having to activate the whole sharing function? 
Edit:
The crazy thing is that activating the sharing function overrides the restricted contacts app. Because as soon as sharing is allowed for a group, all users in that group have access to the entire system address book.
Solution:
OK, I have the solution, but the disadvantage is that even admins can no longer access the system account address book. For me, that’s a small sacrifice. And contacts still work, as does Teams. The search is now just globally deactivated.
For example, users in Talks can upload files in group chats and chats, but cannot write to anyone privately.
