For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:czanik:syslog-ng-stable/openSUSE_Tumbleweed/home:czanik:syslog-ng-stable.repo
zypper refresh
zypper install syslog-ng
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:czanik:syslog-ng-stable/15.6/home:czanik:syslog-ng-stable.repo
zypper refresh
zypper install syslog-ng
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:czanik:syslog-ng-stable/15.5/home:czanik:syslog-ng-stable.repo
zypper refresh
zypper install syslog-ng