Long story short, lwjgl2 uses xrandr to populate an hashmap and picks always the first key as primary monitor, this is not always the case and can cause jme to crash with
“Unable to find fullscreen display mode matching settings”
when trying to use fullscreen.
This fixes it: GitHub - riccardobl/lwjgl2-primarymonitor-patch-xrandr: A java agent that makes lwjgl2 use the correct primary monitor on Linux.
This is not jme fault, but i thought to share it here since i know others had or have this issue and lwjgl2 seems deprecated in favour of lwjgl3 so i doubt we will get a patch from them…