I’m unable to remove my payment method

Unless you have a NONE option in the payment methods of your account details, you usually have to provide a different payment method before you can remove the current one.

Also, unless you have a NONE option in the payment methods, you usually have to have a valid payment method entered in your account details. Even for free apps or to update apps.

M1 Mac mini, macOS 12.5; Watch, series 5 GPS/cellular, watchOS 8.7; iPad Pro 2nd Gen, iPadOS 15.6; iPhone 12 Pro, iOS 15.6; TV 4th Gen, tvOS 15.6; HomePods, audioOS 15.5.1 and Airport Express w/ Airplay 2