For standard run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:rwill:branches:Base:System/standard/home:rwill:branches:Base:System.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:rwill:branches:Base:System/15.5/home:rwill:branches:Base:System.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:rwill:branches:Base:System/15.4/home:rwill:branches:Base:System.repo
zypper refresh
zypper install grub2-x86_64-efi