Different payment methods for different apps

Not easily. You can enter multiple payment types into your payment list and move each one to the top of the list as you purchase the different apps or subscriptions come up for renewal. Note that account balance is always charged first so if it is you intention that it not be used for an app you will have to ensure your balance is empty when the app comes up for payment and instead forced to a card.

This document explains how to add a payment method to your Apple ID on a anddisply all the payment types you have entered--> Add a payment method to your Apple ID - Apple Support

Not without manually reordering them each time, or moving some to a Family Sharing subaccount and redeeming gift cards into it.

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