ForceJava21

What is this mod?

ForceJava21 is a rather unusual and even somewhat strange mod that forcibly requires Java 21 to launch Minecraft. If you're playing on version 1.16.5, you'll additionally need Forge version 36.2.41 or higher.

How does the forced check work?

When attempting to launch the game with Java 20 or an older version, an error message will immediately appear in the logs, and Minecraft will stop working. Here's what this warning looks like:

Java 21 (and Forge 36.2.41+) is required to launch Minecraft.
Current Java version: yourJavaVersion. Current Forge version: yourForgeVersion
Recommended distributions: 
Zulu: https://www.azul.com/downloads/?version=java-21-lts&package=jdk#zulu
Oracle: https://www.oracle.com/java/technologies/downloads/#java21
Temurin: https://adoptium.net/temurin/releases/?version=21

Is it possible to run 1.16.5 Forge with Java 21?

Yes, it's quite possible! Details about the technical implementation can be found in the corresponding pull request on GitHub.