The WebAuthn spec defines a WebDriver extension capability to assist in automation and testing Web Authentication here: https://www.w3.org/TR/webauthn-2/#sctn-automation This will aid web developers writing tests against WebKit as well as increase the number of WebAuthn WPT tests that can run, as many of the failing ones are due to a lack of virtual authenticator support in WebDriver.
<rdar://problem/83895724>
The fix for this issue was needed outside the WebKit project, therefore this is being resolved as 'Moved'. This issue should be fixed in the iOS 15.4 Beta.