For standard run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:michael-chang:grub:2.12rc1/standard/home:michael-chang:grub:2.12rc1.repo
zypper refresh
zypper install grub2-x86_64-efi
For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:michael-chang:grub:2.12rc1/openSUSE_Tumbleweed/home:michael-chang:grub:2.12rc1.repo
zypper refresh
zypper install grub2-x86_64-efi
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:michael-chang:grub:2.12rc1/15.5/home:michael-chang:grub:2.12rc1.repo
zypper refresh
zypper install grub2-x86_64-efi
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:michael-chang:grub:2.12rc1/15.4/home:michael-chang:grub:2.12rc1.repo
zypper refresh
zypper install grub2-x86_64-efi