For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mnhauke:games/openSUSE_Tumbleweed/home:mnhauke:games.repo
zypper refresh
zypper install vkquake
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mnhauke:games/15.6/home:mnhauke:games.repo
zypper refresh
zypper install vkquake
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mnhauke:games/15.4/home:mnhauke:games.repo
zypper refresh
zypper install vkquake
For 15.3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mnhauke:games/15.3/home:mnhauke:games.repo
zypper refresh
zypper install vkquake