Tried to renew a certificate, but the Keychain Access icon is gone?
macOS Sequoia 15 and later changed how you launch it.
A “Passwords” app is now the main thing displayed, and Keychain Access—which engineers need—seems to have been hidden.
The underlying data is probably the same, but the Passwords app is a simplified interface for usability.
How to access it
Hit Command + Space to open Spotlight and type “key”—the icon will show up.