For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:lorenz:filesystems/openSUSE_Tumbleweed/home:lorenz:filesystems.repo
zypper refresh
zypper install zfs
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:lorenz:filesystems/15.5/home:lorenz:filesystems.repo
zypper refresh
zypper install zfs
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:lorenz:filesystems/15.4/home:lorenz:filesystems.repo
zypper refresh
zypper install zfs