How to disable "allow guests to join via link" option in Talk conversations

Hi, I am new to NextCloud and I have installed Nextcloud v 24.0.4 on my server recently.
I want to use it for Organizational chat and do not want to allow members of my organization to initiate Public Conversations.
I see the option in Talk app, while creating a new conversation, “allow guests to join via link” - I want to disable it completely or at least for certain groups of users.
Can anyone guide me, how to do it ?

Thanks in advance :slight_smile: