Hello,
Yes, you can make your group as closed group. But closed group require group admin to approve member join request. If you want to maintain the group as public group, then you will need to customise your user's group app. To do this, open the file 'JOOMLA/media/com_easysocial/apps/user/groups/groups.php' and look for below code at line 301:
if (!$group->canViewItem()) {
return;
}
and replace the above with:
if (! $group->isMember(FD::user()->id)) {
return;
}
The above code will check if the users is a group member or not. If the user is not a group member, that particular stream item will not show to user.
Hope this help and have a nice day!