I tried one more time to build with openSUSE on WSL with the packages qemu-tools, gptfdisk, e2fsprogs, squashfs, xorriso installed. This time it completes making the .raw file but it fails after “Creating bios image”.
[ ERROR ]: 14:19:42 | KiwiBootLoaderGrubDataError: grub path i386-pc not found in ['/usr/share/grub2/i386-pc', '/usr/lib/grub2/i386-pc', '/usr/share/grub/i386-pc', '/usr/lib/grub/i386-pc']
[ INFO ]: 14:19:42 | Cleaning up FileSystemSquashFs instance
[ INFO ]: 14:19:42 | Cleaning up BootLoaderConfigGrub2 instance
[ INFO ]: 14:19:42 | Cleaning up InstallImageBuilder instance
So in conclusion I think the easiest way for anyone on Windows is to just disable WSL (if enabled), install openSUSE in VirtualBox and build from there.
Or maybe this approach using Docker? I didn’t try this myself.