For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ecsos:server/openSUSE_Tumbleweed/home:ecsos:server.repo
zypper refresh
zypper install php7-gd
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ecsos:server/15.6/home:ecsos:server.repo
zypper refresh
zypper install php7-gd
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:ecsos:server/15.5/home:ecsos:server.repo
zypper refresh
zypper install php7-gd