They exclude CCs. They have a card reader but they either have a sign saying, or the vendor will simply say, “keine Kreditkarte”.

So a lot will have in their contract with their processor that they actually can accept Visa/Mastercard, so the sign is there to put you off.

But actually a lot don't, and when you try to pay, even contactless, with a non-Girocard, it won't work.

Visa and Mastercard don't magically let you on their network because you have a card machine.