Well, the real problem is iCloud Keychain is essentially a "black box" system. Apple does use AES encryption in various parts of their security architecture, as documented in their security white papers. But we can't confirm the specific implementation details for iCloud Keychain.
And you should also know...
Best practices for password storage use one-way hash functions (like bcrypt, Argon2, or PBKDF2).
And you should also know...
Best practices for password storage use one-way hash functions (like bcrypt, Argon2, or PBKDF2).