I made a temporary solution by changing the text on the buttons below the service/testimonial:
The button for the previous entry now displays “Weiter” which is “next” in german
The button for the next entry now displays “Zurück” which is “previous” in german

It’s a little uncommon to have the “next” button on the left and the “previous” button on the right, but I think it’s a smaller drawback compared to having an entry navigation which navigates in a reversed way to the archive navigation.

On mobile devices it’s actually a user friendly navigation method, since the fake “next” button is displayed above the fake “previous” button.