For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mcepl/openSUSE_Tumbleweed/home:mcepl.repo
zypper refresh
zypper install nethack
For openSUSE Factory zSystems run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mcepl/openSUSE_Factory_zSystems/home:mcepl.repo
zypper refresh
zypper install nethack
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mcepl/15.6/home:mcepl.repo
zypper refresh
zypper install nethack