Disable SEO (Bronze or higher):
When SEO is disabled, your publication will not be indexed by search engines and appear in search engines like Google. Your publication will only be accessible from its sharing link.
To disable SEO go to the group options via the three dots next to the group name and select Viewer Customization. Under the Advanced settings tab you'll find the option to disable the SEO.
NOTE: If your publication has already been indexed by Google, before you disabled SEO, it will remain visible via Google.
Password-protect publications (Silver plan or higher).
For an extra layer of security, you can add a password to your publication. Anyone attempting to access your publication will have to enter a password to view it.
To secure a publication with a password go to the publication's settings (via ••• or click on the title in the overview) and enable Secure this Publication with a password.