Rito_kun Said:
"iCloud Keychain: I have saved someone else’s password in Apple password/keychain. I try to remove it but it says
deleting this password will remove from iCloud password and keychain on all devices'. Does that mean my iCloud or device is the only two to get affected?"
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Removal of a Keychain Item:
That means all devices associate to your Apple Account will no longer have access to this password, and you'd have to add it back on your own. As to how you have their information, is anyone's guess. So, remove it, and let this person, know that you have done so.