[OtomotO]

Ah, yes, thanks for clarification.

So I would just sync the keys locally or via some browser-extension and then on each device be responsible to provide the "secret" (e.g. my face or fingerprint) in a readily way to unlock said key, yes?

[searchableguy]

Yes, depending on the platform.

See apple passkey page: https://support.apple.com/en-in/HT213305