In the GhostContacts app, you can add contacts to the secret list, there is support for dark and bright topics, localization, export and imports of CSV contacts, an emergency password is supported to reset the list of contacts if the user suddenly requires a regular password for entering.
Application online:
https://demensdeum.com/software/ghost-contacts/
Github:
https://github.com/demensdeum/GhostContacts