Why can't I set my Github Pages as Private?

I am trying to set my Github pages as private and only allow a few people to view my pages.
According to this article, I can do this by setting the repository private Access control for GitHub Pages | GitHub Changelog

But when I did it, I see no dropdown option for setting my Github pages as private, as shown in the article above. Instead, I see a yellow box reminder:

This article can help you:


GitHub Pages sites are publicly available on the internet by default, even if the repository for the site is private or internal.
If your project site is published from a private or internal repository owned by an organization using GitHub Enterprise Cloud, you can manage access control for the site.
Access control for GitHub Pages is only available on GitHub Enterprise Cloud.
If you are on GitHub Enterprise Cloud and still can’t access the feature, please log a ticket with us at GitHub Support.