You have a debit card.
You wish to no longer use the debit card.
You wish to remove the debit card from your Apple ID.
Do you wish to discontinue all payments and discontinue all subscriptions?
Or are you looking at discontinuing subscriptions only because you are trying to remove the debit card, and got that error?
If you wish to (also) discontinue iCloud, here is how: Downgrade or cancel your iCloud storage plan - Apple Support
If you solely wish to change payment methods, add the new payment method first, and only then remove the debit card. This payment-swapping approach will avoid having to cancel all existing subscriptions, if you wish to preserve those subscriptions.
Alternatively, use the Get Support link in the upper right of this webpage, and work with Apple to make the required changes.