FYI, Claris has significantly expanded their response at https://support.claris.com/s/answerview?anum=000035819&language=en_US and provided more information on older versions.
If you want a more in-depth analysis, I've been collating all the community findings I'm aware of, along with our research, in a blog post on fixing the Log4j exploit on FileMaker Server.
FileMaker Server 16 is not vulnerable to these two newest Log4j (2.x) exploits, so you probably won't be compromised by the majority of botnet activity going on right now. However, FMS 16 does use an older Log4j (v1.2.15) that is no longer maintained and has active Remote Code Execution vulnerabilities of its own. You should *definitely* check out the mitigation steps in our blog post and prioritize upgrading to FileMaker Server 19.