Hi Clark, ventilation could be part of the answer but I think generally most Europeans spend more time outdoors than British people. British people tend to be fatter and suffer from more diabetes and eat more processed foods.
If German people are currently getting infected at 1/40 th the rate British people are currently getting infected, this is something worth looking into more deeply.
Possibly it will be the Delta that is the largest factor.
but there may be other contributing factors, which would be good for u