Is a third credit card worth it or does it do more harm to SCHUFA than it does?

I generally value the best possible SCHUFA, as I may also want to finance real estate in the next few years. I currently have two credit cards: Payback American Express and Amazon Visa. I used to also have the Klarna credit card and a credit card from easyBank, but I canceled them because I was afraid that too many credit cards would worsen my SCHUFA score. Now I'm thinking about whether a third card (e.g. because of travel benefits, cash