other people have answered your question about syslog-ng and i thought i should share something that i wish someone had shared with me when i was studying up to on a job as an ELK administrator about a decade+ or so ago.
if you have familiarity with any of the non-journald based logging (eg rsyslog, syslog, etc.) and basic networking (eg tcpdump, traceroute, etc.) your experience will translate into syslog-ng well and there's significant syntactical differences between the versions since it's been around for decades now.