Hello lucas, thanks for the tip you provide there (https://github.com/lategoodbye/rpi-zero/issues/43#issuecomment-619974846)
As I can see in this Post here you have a working Image with Kernel 5.5 without USB Support. I need the USB Support. So I try to Build a Image with Kernel 5.6 with the result that the Image does not boot. (see https://lists.debian.org/debian-arm/2020/04/msg00023.html) It seems that the uboot is not build properly. The Serial console show a lot of � (Replacement character). basti