RequestAutocomplete is indeed deprecated and Stripe is using PaymentRequest (which doesn't do anything fancy except pull your CC info from Chrome autofill for the record, so no one-time card for the payment).

RequestAutocomplete had some weird quirks that made adoption slow and full of friction. You're right to say that PaymentRequest is a fixed RequestAutocomplete in most regards, and it's amazing (I'm biased though, I'm one of the people implementing it on desktop Chrome :) ). It's being implemented by all major browsers too!