Your Netflix passkey is not the same as your passkey to other services. It's generated as soon as you enroll the passkey with Netflix (by calling "navigator.credentials.create()") and is identified by an opaque handle and also the public key (this is important, because you never get the public key again so you must keep both of these: the ID, and the Public Key, otherwise you can't verify a challenge-response, since you're only given an ID and a Digital Signature at that point).
For a site to use a passkey it calls "navigator.credentials.get({ publicKey: { challenge: ..., rpId: "<same_id_as_used_when_creating_like_netflix.com>" }, mediation: "silent" })"
Which returns the key ID and a signed version of the challenge, or an error.
Everywhere you authenticate you have one or more keys, identified by these opaque handles which are stored in the User Agent and associated with some mechanism for performing digital signatures with that unique key. The User Agent, generally, has to store and distribute this information if you want to use the same passkey across multiple devices -- even if you're using a Yubikey (because, again, it's not storing the key being used for the digital signature, it's storing a private key which is used in the process of generating the digital signature, but not the passkey's actual private key -- i.e., the secret part of the public key generated earlier)