For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Boria138:PortProton/openSUSE_Tumbleweed/home:Boria138:PortProton.repo
zypper refresh
zypper install portproton
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Boria138:PortProton/15.5/home:Boria138:PortProton.repo
zypper refresh
zypper install portproton
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:Boria138:PortProton/15.4/home:Boria138:PortProton.repo
zypper refresh
zypper install portproton