Otherwise, anyone who is not following you doesn’t have to be blocked and will not be able to view your posts. Tech Crunch reported that this had been done more than 10 years ago.

If you are blocked, Instagram prevents you from mentioning or tagging the other party's username. You can check to see if you are blocked by mentioning or tagging them in your posts.

Even after being an admin, if you are not able to add him to the group, it means that you have been blocked. Apart from this, the user will also not see the last seen, online status, typing indicator.