

There is no good reason so send the passwors itself to the server. Send the hash and you will have a fixes length of data to send anyway.
And even if insist in sending the password over the wire, there is no problem on the backend to handle longer passwords than that, so that no one will run into a limit in practice. We’re talking about bytes here, not even a kb.
You seem to be falling for what the author was writing about. Only because you could technically try to use keepassxc to store passkeys, that does not mean that it will work. You see passkeys were build in a way the service you’re trying to login to can decide if they accept your keepassxc for passkey storage or not. It looks like you are in control when you are actually not.