For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Virtualization/openSUSE_Tumbleweed/Virtualization.repo
zypper refresh
zypper install libnbd
For openSUSE Slowroll run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Virtualization/openSUSE_Slowroll/Virtualization.repo
zypper refresh
zypper install libnbd
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Virtualization/15.6/Virtualization.repo
zypper refresh
zypper install libnbd
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Virtualization/15.5/Virtualization.repo
zypper refresh
zypper install libnbd