I’m afraid the ‘who can see’ and ‘who can use’ tag group options have never had an effect on the topics they’re applied to, only the visibility and use of the tags themselves. So if you have a tag group that’s only usable and visible to admins, applying a tag from it will not block the topic from everyone else - but your non-admin members would not be able to see the tag you’d added to it.
You can add them to your default tags muted setting, though this just makes the topics a little more obscure to find rather than putting them behind a permission-style setup as we have with categories.