Hello, I actually found another way to fix this and it appears to have been working for a long time now. I got so frustrated that I decided to put money on my PayPal balance to order something. After this order, only 1 euro remained in the PayPal balance. Since then, every time I go to check out it shows my card and the balance and I can just choose my existing card. I've never gotten the 'add a card' screen again. Hope it works for you too!
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