L0stGuyNL These errors have more to do with the kernel source and the distro you are compiling this on, rather than the tutorial itself.
Here are the probable relevant errors from your logs:-
make[1]: *** Keine Regel vorhanden, um das Ziel „debian/certs/debian-uefi-certs.pem“,
benötigt von „certs/x509_certificate_list“, zu erstellen. Schluss.
make[1]: *** Es wird auf noch nicht beendete Prozesse gewartet....
Google to find out the source of these errors and chances are you will find a fix too. If not, let me know what you actually find after googling and I will try my best to help.