some password managers can pretend to be a passkey. but I don't use them because it requires finicky brittle configuration (and docs lookup whenever you want to redo it).
if passkeys had a simple text challenge response text option it would be fine, you would basically be using something like PGP logins. and would be easy to implement in a password manager interface.
as a result, I have zero interest in passkeys. a pity as it could have been useful (cold storage password manger + physical passkey). you can never trust any service to honor "backup" login options, got burned once for "suspicious activity". that is, if you lose a login option (passkey is lost) they can demand it in the future to "verify".
And don't you just love the fact that now Apple and Google and Microsoft have MORE control of my identities across the web?