This extension has been removed from WebAuthn Spec here:
w3c/webauthn#1386

It could still be used, but there was no concrete usage of it.
If it were to be replaced, we should probably consider the payment
extension:
https://w3c.github.io/secure-payment-confirmation/

FIDO2.1 specification and conformance tools enforce that:
The authenticator generates two random 32-byte values (called
CredRandomWithUV and CredRandomWithoutUV) and associates them with the
credential.

This field is optional in FIDO2 in some cases, but required in FIDO2.1.
Some browser enforces it, see
mozilla/authenticator-rs#319
As not including it is an unnecessary optimisation, we rather always put
it if it causes compatibiity issue.