What you're talking about seems to be what the article would call a "non-resident" key, whereas this commenter is specifically asking about "resident" keys.
Or, if you think you are describing resident keys, then you need to reconcile,
> This design allows you to have as many keys as your mass storage will allow you to save.
with the OP: the article states that to be roughly "20", and people tend to have more than 20 logins, and that is the reason the person you're responding to is asking the question they're asking.
What I'm saying is if you look at the sequence diagram for the resident key, at step 3 there's no requirement to have the keys stored in the security key: you can save an Rp to token mapping in the client outside and it's still considered a resident key.
I think what I'm saying here is that resident means resident to the client, not necessarily resident to the enclave. I took a peek at the spec and they define resident keys as being part of the "client platform" which they take care to clarify as "A single hardware device MAY be part of multiple distinct client platforms" https://www.w3.org/TR/webauthn-2/#client-platform
Or, if you think you are describing resident keys, then you need to reconcile,
> This design allows you to have as many keys as your mass storage will allow you to save.
with the OP: the article states that to be roughly "20", and people tend to have more than 20 logins, and that is the reason the person you're responding to is asking the question they're asking.