X is deprecating Circles as of Oct 31st, 2023. After this date, you will not be able to create new posts that are limited to your Circle, nor will you be able to add people to your Circle. You will, however, be able to remove people from your Circle, by unfollowing them as described below.
How to remove people from your circles
Log in to https://x.com
Go to the account that is in your Circles and unfollow them.
They will no longer be in your Circle. They can no longer see your past Circle Posts.
Follow them again, if you wish, they will not be added to your Circle.