You can choose whether or not to display content in search engine results through the "Release Settings" of the Public Folder.
Related:
What items can be configured in folder settings?
https://help.teachme.jp/hc/en-us/articles/14419216152985
View and update folder settings (Web Browser)
https://teachme.jp/8/manuals/4929542
What is Outside Release (Public Folder).
https://help.teachme.jp/hc/en-us/articles/900006443043
*The default setting is "OFF".
When you enable "Display in search engine" in the "Release Settings" screen, both the manuals within the folder and the folder itself will become visible in external search engine results.
Once enabled and content becomes indexed by external search engines, it cannot be removed from search results even if you uncheck and save the setting later, as it will have already been registered in the search engines' databases.
Please note this in advance.