Oral exams don't scale at the beginning with hundreds of students per course, agreed. So make them in-person written exams, German universities managed that just fine a few decades ago. Oral exams were reserved to advance from Grundstudium (basic) to Hauptstudium (main).

In my very limited experience (I have German major degrees in Informatik and Philosophy, I was a TA for Logic in Philosophy) the more advanced the topic the thinner the attendance anyway.