In Germany being able to pay with a card is not a standard. And from that subgroup of places accepting cards, a big number of them will accept only Giro (German card standard). Visa/MC is far from being universally accepted and AMEX is even rarer.
That changes of course, but mostly in big cities' centers (Covid accelerated things in Berlin). I hope businesses catch up with the new wave of payment terminals like iZettle and SumUp - they support all these different cards without a problem