He asked the same question 3 weeks ago and received an answer [BUG] Not detecting Java on Linux (Lubuntu 19.04)
Java 13 is not supported (yet). Java 11 is a LTS version, default on Ubuntu and can be used. If we want to keep that ticket i would requalify it as an improvement, minor and name it as “Add support for Java 13”. Although i’m not sure if we should do this, as it will be dead soon and Oracle will release 14, 15, 16 and so on with their weird release cycle. You can’t keep up with every new short time release. 11 is enough for a while.
Oracle might introduce changes to APIs that can brake something in Openfire (hence the new major version of Java and not a point release). So, we can’t blindly support any version, because it would only seem that Openfire works, but it would run into some issues. So it has to be tested for every major version and adjustments to code be made if necessary. Although in this case error is misleading, as Openfire does work with Java 11. So this check can be fixed to provide correct min version.