A URL fragment is the part after #. The HTTP specification prohibits browsers from sending fragments to servers. The server that delivers the page never receives the content, never knows which site you are viewing, and has no way to find out. No content is collected, stored, or logged. The privacy is structural.
A site that was never put on a server can never be taken off one. There is no account to suspend, no host to pressure, no platform that can decide your content should not exist. Each copy of the link is a complete copy of the site data.
Site creators can encrypt the URL itself with a password. Even possessing the link reveals nothing about what is inside.