For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/filesharing/openSUSE_Tumbleweed/filesharing.repo
zypper refresh
zypper install rtorrent
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/filesharing/15.6/filesharing.repo
zypper refresh
zypper install rtorrent
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/filesharing/15.5/filesharing.repo
zypper refresh
zypper install rtorrent