I want to turn off me having to have a payment method to download anything on my iPhone

Sorry but it can’t simply be “turned off.”

If you are being prompted to add a payment method, you must do so in order to continue.

See available options here:

Payment methods that you can use with your Apple ID - Apple Support

Even in happenstance, should you fully apply an authentic payment source

to your Apple ID and then update or refresh the system; leaving the security

code from the credit/debit off..

..The next time, when you enter into that section, it may surprise you (if left

alone and not used for some months, as I did) all kinds of things want to be

done then. Even if only revisiting 'turned-off' feature; reset to the least level.

And where no 2FA had been, the system's intent is to update your products.

..So that may or not be delightful; to an old school cabin dweller w/ wood heat..

Newest products automatically enroll your account to higher than previous levels.