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