This is a reported bug with Magento. It appears to have been around since v2.3.5
But that is passed to PHP despite PHP expecting a more generic payment method ...
Payments are tightly coupled into Magento checkout. Quote, orders, billing address - all of these use payment.
You might create a custom payment method that is based on Cash on Delivery - just with a different name/comment. Additionally, you can hide payment input field, so the Customer is not distracted by one radio button.