For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:brassh/openSUSE_Tumbleweed/home:brassh.repo
zypper refresh
zypper install steam
For graphics run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:brassh/graphics/home:brassh.repo
zypper refresh
zypper install steam
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:brassh/15.5/home:brassh.repo
zypper refresh
zypper install steam
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:brassh/15.4/home:brassh.repo
zypper refresh
zypper install steam