The launcher uses the system Java runtime, even if Java 8 is installed.

What I expected to happen was...:

The launcher should check if

"/usr/lib/jvm/java-8-oracle/jre/bin/java"

or

"/usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java"

exists and try to use those before reverting to using "/usr/bin/java" (which is probably going to be Java 10 or 11 on most linux installs).

As an alternative, you could at least inform the player that he is not using an optimal version of java and leave the task of setting the Java executable launch option to the user.

Steps to Reproduce:
1. get a fresh install of linux.
2. run apt install default-jre
3. run apt install openjdk-8-jre
4. install the minecraft launcher from: _https://launcher.mojang.com/download/Minecraft.deb_
5. the launcher will use Java 11, even though Java 8 would be the better option