Hey, thank you.

In the meanwhile I figured out a few things, for example the prints I trigger with Octoprint over the USB-Connection are worse then the prints from the SD-Card itself and also the old Cura 3.3.0 Version from the manufracture seems to work also better then the newer versions of Cura. So there is a high chance that the main problem is not the PETG Filament itself. This 3D Print stuff is very complicated , but at least its fun to troubleshoot.