Ok, I admit it, I mistakenly thought there was a tie between Apple Pay and payment to the Apple App Store. Turns out these are completely unrelated. I twizzled the Apple Pay payment order to use my normal Visa card, but Apple App Store and Apple Subscriptions kept on going to a different card.
Well, I'm an idiot, turns out there is a completely different UI for setting the order of charge for Apple subscriptions and this lives in the App Store. It's a little confusing since I don't think of Apple TV subscriptions as App Store things. So for instance, a Disney+ subscription actually takes its payment methods from the App Store and not the Apple Pay order. Silly me.
Once I figure this out, I went on my Mac to the App Store and clicked on the lower left icon in Big Sur to get to the Apple ID summary and then "Manage Payments" and I discovered that my card had expired and had an invalid number. So they don't pull this data from Apple Pay at all. Fixed and good to go. You are warned 😃