How does 3D Secure v2 works through while waiting for full deployment?

The payment gateway initiates the process of 3D Secure v2 authentication.

If the card is 3D Secure v2 enrolled, the 3D Secure v2 process continues.

If the card is not 3D Secure v2 enrolled, the payment gateway proceeds with cardholder authentication in 3D Secure v1 mode.