Keychain Access has been in MacOS for decades …
Where – alongside all the passwords, keys, and certificates that the system keeps there, a user could keep their own Secure Notes. And create our own, custom keychains. Over time, I’ve created multiple custom keychains to keep completely different sets of passwords (and other information) in Secure Notes separate for different projects & employers. I.e., I used one MacBook instead of multiple paper notebooks full of secrets.
Didn’t see much functional change when iCloud Keychain was added; seemed like Just Another Keychain in Keychain Access.
Now we have password managers; wish I’d had 'em years ago. I’ve tried several, and am now moving my Secure Notes items into password manager entries. Awkwardly – since the way I organized my passwords in Secure Notes doesn’t really doesn’t export; I have to retype things manually. And slowly – because I have roughly a 1,000 Secure Notes (yes, a lot are obsolete, but I still have to check them).
For anyone else in similar circumstances, who might be wondering if you need to convert from Security Notes in keychains in Keychain Access, now the answer is Yes.
Because as of MacOS 15.3.2 (or maybe …1; happened in March, anyway) Keychain Access seems to not allow creating new Secure Notes in any keychain. [Existing Secure Notes remain, for now at least.]
So, we can no longer add new passwords or other secure info as a Secure Note onto keychains in Keychain Access. For new entries, I hope you’ve found and use a password manager that you’re comfortable with.