Another remark (although this is in the area of yast2-bootloader in which I'm not the biggest authority). YaST (or Agama, for the discussed case) does not explicitly call efibootmgr or any similar tool to ensure the system boots from the installation disk on next boot. That's delegated to the corresponding command used to install Grub. See https://github.com/yast/yast-bootloader/blob/master/src/lib/bootloader/grub_install.rb#L30