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Google will now make passkeys the default for personal accounts
(arstechnica.com)
This is a most excellent place for technology news and articles.
It's not quite unique to a specific device. You can store your private key in a password manager or something similar, and then access it from other devices
Depends on your personal choice. You can definitely limit them to a single, hardeneddevice if you want the highest level of security.
For most users and most situations, a synced solution will be preferable.