For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:xorcue/openSUSE_Tumbleweed/home:xorcue.repo
zypper refresh
zypper install stumpwm
For openSUSE Leap 15.1 ARM run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:xorcue/openSUSE_Leap_15.1_ARM/home:xorcue.repo
zypper refresh
zypper install stumpwm
For openSUSE Factory ARM run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:xorcue/openSUSE_Factory_ARM/home:xorcue.repo
zypper refresh
zypper install stumpwm