Do I have to add a card

No, you don't have to, but if you want to download anything that has a financial obligation such as a subscription linked to it, you will have to. I don't have one linked to my account but the only apps I download are completely free.

"Some purchases might require that you have a credit card on file, even if you use your Apple ID balance to make the purchase." - from: What you can buy with your Apple ID balance --> https://support.apple.com/HT211187

For a variety of reasons Apple will almost always require a functional payment method such as a credit or debit card be present when downloading anything from the iTunes or App Stores that isn't totally free, even if the item will be paid for with Apple Account balance. The only solution to satisfy this requirement is to add a valid payment method.

This document explains how to 'Change, add, [review,] or remove Apple ID payment methods' on a Mac or Apple mobile devices; click here --> https://support.apple.com/HT201266

Create or use an Apple ID without a payment method - https://support.apple.com/HT204034

However, despite the title of the previous document, the document 'If you can't remove your last payment method or use no payment method with your Apple ID' ( https://support.apple.com/HT203905 ) mentions, "if you're using an existing Apple ID with the App Store for the first time, you must provide payment information." I guess you can just remove it again afterward.

Log into your account in the App Store/iTunes and you should be able to change/verify it there. Or you can click the blue Edit payment methods in the article below. When signed in and the page loads, you will be on the credit card page. After updating that, click the Go Back button at the lower left and you will be on the address page. If you have a subscription, you need to add the new card, and then promote it to the primary payment method before you can remove the old card.

Apple ID payment information - change.  *