For openSUSE Leap 15.3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:yudaike/openSUSE_Leap_15.3/home:yudaike.repo
zypper refresh
zypper install gtg
For SLE 15 SP4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:yudaike/SLE_15_SP4/home:yudaike.repo
zypper refresh
zypper install gtg
For SLE 15 SP3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:yudaike/SLE_15_SP3/home:yudaike.repo
zypper refresh
zypper install gtg
For SLE 15 SP2 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:yudaike/SLE_15_SP2/home:yudaike.repo
zypper refresh
zypper install gtg