You have already discovered the related ticket in JIRA, so you know that this is a known bug and nobody on the team knows how to fix this. Until some experienced java developer for macOS provides a fix, you can use older version of Openfire https://github.com/igniterealtime/Openfire/releases
there is a startup script (openfire.sh) in the openfire install folder. you can run this script to manually start OF. you may need to set JAVA_HOME if its not already set.
I have been trying for days to get Openfire running on 10.15.5. Would you mind sharing how you did it? I followed the commands that gregwang posted but I can’t get openfire to start. I would really appreciate the help - thanks!
One more thing that I just remembered I faced was permission issue. I just changed permission of the folder to 777 (since it is a local test installation so it was not an issue. But don’t do it in production)