Did you fix your system in the meantime? Or are you still unable to boot?
I installed openSUSE using Legacy booting, but I’m not 100% sure.
Okay, that seems likely. This problem is less likely to happen with UEFI booting, though you can have different problems.
Here’s a wild guess. Sometimes openSUSE install booting from the extended partition. That works well, but it is not a place from which booting is fully supported. So some other software (could be Windows software) might have removed that boot code from the extended partition.
If you still have that problem, try google for “Super Grub Disk” (or, I think you need “Super Grub2 Disk”). That can probably boot you into your system. And then you can use Yast bootloader to reinstall booting.