What should be implemented to limit what can be displayed in developer sources?

I’ve spent about a month on this topic alone researching and I was wondering how do some hosted WordPress sites have the ability to hide all folder structure (wp-content, wp-includes, themes, plugins) except for the index file? I’ve tested and can execute a folder rename but I’ve been trying to search for a way, without a plugin, that will allow me to hide all this resulting in the display of only (index). Can this be done via the .htaccess file or is this an existing function, class, or hook that will allow this?