There is no way to exclude users from seeing something. You can only configure who is allowed to see something.
So you need to change the settings of all categories to show most of them to a group where your new group of users is not a member of, and then you add the other group only to their category.
Depending on why you want this, muting most categories for the group of users could work. That simplifies the interface, but of course, it doesn’t prevent access. So it’s not helpful in cases where you want information not to be available for them.