How and why to use FIDO Security Keys for Apple ID

In a world that needs Apple’s recently-improved Lockdown Mode to protect good people against bad ones, high-risk individuals should consider using physical security keys to protect their Apple ID.What are Security Keys and what do they do?
Security keys are small devices that look a little like thumb drives. Apple at WWDC 2020 confirmed plans to support FIDO authentication beginning with iOS 14 and macOS 11; now, with the release of iOS 16.3, iPadOS 16.3, and macOS Ventura 13.2, Apple let