You can have a credit card / debit card on file and an Apple Account balance.
You need to set your Apple Account balance as your default payment method, your default payment method will be used first by Apple when you need to make a payment.
Apple always charge my iCloud subscription from my Apple Account balance (Store credit).
Keep in mind:
Some purchases might require you to have a credit card on file, even if you use your Apple Account balance to make the purchase.
See -> What you can buy with your Apple Gift Card or Apple Account balance
What you can buy with your Apple Gift Card or Apple Account balance – Apple Support (UK)
- You can't use your Apple Account balance to send gifts or gift cards.
- If you use Family Sharing, your family members can't spend your Apple Account balance. Funds that you add to your Apple Account balance are only available to you. Find out more about how purchases are billed to your Apple Account balance.
- Some purchases might require you to have a credit card on file, even if you use your Apple Account balance to make the purchase.
