After extracting the 6.09.01 ZIP package from the website, entering the working directory of it, and running "./pcgen.sh", on both Arch Linux and Linux Mint, with various versions of OpenJDK/OpenJFX and Oracle Java, PCGen fails to start. Below are various samples of output with different configurations:
Arch Linux, Oracle Java 13:
OpenJDK 11 with OpenJFX 11 installed:
Arch Linux, OpenJDK 12 with OpenJFX 12 installed:
Arch Linux, Oracle Java 13 using "-Dprism.verbose=true -Djavafx.verbose=true":
I also tried it on the Linux Mint live CD, which has OpenJDK 11, and the output looked the same as the OpenJDK 11 output above.
Arch Linux and Linux Mint, with various versions of OpenJDK (with OpenJFX) and Oracle Java