For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/X11:windowmanagers/openSUSE_Tumbleweed/X11:windowmanagers.repo
zypper refresh
zypper install herbstluftwm
For openSUSE Factory ARM run the following as root:
zypper addrepo https://download.opensuse.org/repositories/X11:windowmanagers/openSUSE_Factory_ARM/X11:windowmanagers.repo
zypper refresh
zypper install herbstluftwm
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/X11:windowmanagers/15.6/X11:windowmanagers.repo
zypper refresh
zypper install herbstluftwm
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/X11:windowmanagers/15.5/X11:windowmanagers.repo
zypper refresh
zypper install herbstluftwm
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/X11:windowmanagers/15.4/X11:windowmanagers.repo
zypper refresh
zypper install herbstluftwm