I recently helped my friend install Minecraft Java Edition on his Chromebook using the Google supported linux beta (which is Linux Debian).
He can make a singleplayer world, and it works just fine. He can also start a LAN game which I am able to join.
However, he cannot connect to any Minecraft servers. I tried making my own server and a client using UDP Sockets in Java (this is only to provide context) and my friend couldn't join my games (via LAN), but I could join his.
Same thing occurs in Minecraft. I can join his LAN worlds, but he cannot join any servers/worlds.
He is using the default JDK, which is Open-JDK 11, if that helps.
I have tried making him uninstall java, I have tried making him install java 8 with
sudo apt install openjdk-8-jdk instead of the default-jdk, but it said "Unable to open package". I'm not even sure if this is java's fault. It can possibly be his firewall.
To provide more context, he is using Optifine, and he has tried both Minecraft 1.8.9 and 1.14.4 without success.
When he joins, Minecraft shows this error message:
Internal Execption: java.lang.RuntimeExecption: Unable to access address of buffer
What is the problem, and how can I fix this?