Thanks for your help. I reinstalled openSUSE and now everything works fine.
During the installation at the partition overview I saw that Linux will be installed for EFI booting but I still don’t get where I had the possibility to change this for Linux and Windows. I just installed it (as always) but I never saw the option “Do you want EFI or MBR booting?”.
Thanks for your time again for solving my problem. 