Java/OpenJDK is pretty hard to correctly install, but thankfully, I made a solution: BetterTemurin! It's an installer for Eclipse Temurin (OpenJDK) that sets OpenJDK up so you can use Java apps. Just let it install and everything will be set up. Make sure to read the documentation. You can access it on Gemu by clicking More... then Documentation.
Gemu is maintained by RetroAkaMe and the community