Seahorse is a GNOME application for managing encryption keys and passwords in the GNOME Keyring.

Passbook is described as 'Frontend for Gnome keyring, manage and view secrets used by desktop applications' and is a password manager in the security & privacy category. There are three alternatives to Passbook for Linux, Flathub, GnuPG and GNOME. The best Passbook alternative is Seahorse, which is both free and Open Source. Other great apps like Passbook are GNOME Keyring and Key Rack.
Seahorse is a GNOME application for managing encryption keys and passwords in the GNOME Keyring.

GNOME Keyring is a collection of components in GNOME that store secrets, passwords, keys, certificates and make them available to applications.
Key Rack allows you to view, create and edit secrets, such as passwords or tokens, stored by apps. It supports both Flatpak secrets and system-wide keyrings.