Above the card form sat a sign-up box for Link, a service that stores your payment details for use on other sites. Taking it up meant giving an email address you had already typed in a moment earlier, plus a phone number, and then waiting for a code by text.
It is gone. Checkout now asks for your email once, and your card.
It was also not doing the one thing that might have justified it. Because of how our form is built, Link never received the email you entered, so it could not recognise you from it - returning customers were asked for everything from scratch anyway. And asking for a phone number on behalf of another company sits badly with us in particular.
Apple Pay and Google Pay are unaffected and still appear on devices that have them.