For openSUSE Leap 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:michals/openSUSE_Leap_15.5/home:michals.repo
zypper refresh
zypper install cmake-gui
For SLE 15 SP5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:michals/SLE_15_SP5/home:michals.repo
zypper refresh
zypper install cmake-gui
For SLE 15 SP4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:michals/SLE_15_SP4/home:michals.repo
zypper refresh
zypper install cmake-gui