I've never seen a single sight suggest this either. Many have set up passkeys, but not one has prompted me to create a second. I have downloaded a lot of backup keys though.
Sorry to be on blast here but every time passkeys come up the "use multiple keys" gets said & it's a joke. There needs to be a flow where I can create a passkey & have it replicate to a bunch of devices automatically; the current proposal that users need to gather all their security tokens & add each one is an absolute promise this technology is going to flop.
Choose a passkey provider that supports this then. I use bitwarden. Other people use iOS keychain. Both work great.
Apple and Google both replicate between devices, so there is some replication, within ecosystems. I only need to create a passkey twice per account so I can use both. It’s not a big deal, though replicating between them would be better.
And so I am clearly not locked in. (Not because of passkeys, anyway.) If people think they’re locked in then it’s a “can’t be bothered” sort of lock-in.
Clearly not fantastical since I’m doing it.
Imagine having to use a specific password for each service/device combination. Instead we don’t tie passwords to devices, but to users, to avoid this complexity.
Everything but employer stuff was cheap on Facebook marketplace. I am a bit on the tail end of my friends and coworkers but not by much. It's always been supremely convenient to be able to choose the form and location of my computing device. The cheap devices are largely disposable - I have several layers of backups. It is this perspective that makes passkeys seem strange, a Cartesian joint of many-to-many between my devices and providers that quickly gets... insane.
(This is in context of Passkeys. If your question is ssh, substantially less:)
But that is the entire premise of Passkeys—they remove the complexity, because having individual passwords per device is clearly superior to user-bound passwords, if you don’t need to worry about it and it just works. Hence why, to stay with SSH, you shouldn’t use SSH keypairs, but certificates signed by a CA.
(The added bonus security feature being you could revoke your daily driver if you lose it, while retaining access to your backup. But again there's no actual support for this kind of thing)
Similarly, I wouldn’t copy a private key for ssh to a new laptop. I generate a new one and copy the public key instead. It makes it easier to revoke access to the old computer.
I do think this new spec will sometimes be useful for populating a new password manager, though.