Ditto here. I’ve been able to install multiple versions of java following the instructions at the link below (but not doing the 3rd step to set it as default). But I’m stuck trying to configure MineOS to run a java version other than the default. Some ideas: (1) some type of ‘java version selector’ program that is in the path so that MineOS will run it, which will examine the command line arguments to select the proper version of java to run; (2) a jar program which runs the correct jar program with the correct java runtime; (3) using the command line arguments to somehow fake calling the correct executable using “&&”
Besides adding the feature to MineOS, which would be great, I think that potentially all three of the above techniques could work. I just don’t know enough about java or linux to be able to implement any of them successfully.
Ref: Upgrading to Java 15 from the MineOS Turnkey ISO
Multiple java version support is really needed now that Minecraft 1.17 only runs on Java 16, and prior versions of Minecraft (and/or modpacks) need older versions of Java.