For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/KDE:Qt:5.12/openSUSE_Tumbleweed/KDE:Qt:5.12.repo
zypper refresh
zypper install octave
For openSUSE Leap 15.2 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/KDE:Qt:5.12/openSUSE_Leap_15.2/KDE:Qt:5.12.repo
zypper refresh
zypper install octave
For openSUSE Leap 15.1 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/KDE:Qt:5.12/openSUSE_Leap_15.1/KDE:Qt:5.12.repo
zypper refresh
zypper install octave
For openSUSE Leap 15.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/KDE:Qt:5.12/openSUSE_Leap_15.0/KDE:Qt:5.12.repo
zypper refresh
zypper install octave