For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:avicenzi:proton/openSUSE_Tumbleweed/home:avicenzi:proton.repo
zypper refresh
zypper install protonvpn-gui
For openSUSE Slowroll run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:avicenzi:proton/openSUSE_Slowroll/home:avicenzi:proton.repo
zypper refresh
zypper install protonvpn-gui
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:avicenzi:proton/15.6/home:avicenzi:proton.repo
zypper refresh
zypper install protonvpn-gui
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:avicenzi:proton/15.5/home:avicenzi:proton.repo
zypper refresh
zypper install protonvpn-gui