Once you confirm the operation, the keychain feature will be switched off, and you will no longer be able to store your passwords and other secure credentials on the iCloud server.
Obviously, Apple does vouch for the security of this feature, which is why many users are actively using this feature for their day-to-day use.
There are many other third-party applications that offer these features, but it is recommended that you do a detailed background check on these applications before deciding to use one of them. Personally, if you do need this vault sort of feature to store your credentials, you can simply go for the built-in iCloud Keychain.
