Hmmm see this is how I thought it worked but then Google and Apple providers are syncing passkeys around devices without issue? There are definitely backups and cloud syncs happening. I'm aiming to use an OS agnostic provider like 1password which I'd expect to sync across hardware- but with everything in its infancy I'm not sure how that shakes out.
But tbh that does bring up another concern of mine: I have some 200+ accounts, assuming a passkey world where everything is using them, if a user wanted to change ecosystems it seems they will need to visit every service, edit the account and reconfigure their keys instead of transferring the private keys into the new ecosystem? Sounds like a nightmare!