Regarding userVerification
I have now figured out how to set the userVerificationPreference field. Specifically, I used the init(rawValue:) method of ASAuthorizationPublicKeyCredentialUserVerificationPreference to set the value retrieved from the WebAuthn options userVerification.
registrationRequest.userVerificationPreference =
ASAuthorizationPublicKeyCredentialUserVerificationPreference.init(
rawValue: userVerification.rawValue
)