If you have an ongoing subscription, or one that is canceled but not yet fully expired, you cannot remove the only payment method (account balance does not count for that). You can change the payment method but you will always have to have one on there until you meet the criteria I mentioned.
If you are concerned about that payment method, see if your bank offers sub accounts. We have one we use for travel where we only keep a small amount of money in it. It is part of our main account but is isolated with its own debit card. That way if somebody steals the card we are at most only out a couple of hundred dollars instead of our normal credit card. You would add the debit card with a small amount of money in that sub-account. Just don't forget to check the balance occasionally.
Remove a payment method from your Apple Account - Apple Support
- If you have any active subscriptions, you must have at least one payment method on file other than Apple ID credit.
- You might not be able to remove a payment method if you have a balance due.
- Some subscriptions might not be charged to your Apple ID balance.