If you play Minecraft 1.21.1, choose the NeoForge build of Immersive Engineering. Mixing a Forge-only or older-game file with this setup is a common reason for mod loading problems.
Which loader does 1.21.1 use?
The published ImmersiveEngineering-1.21.1-12.4.2-194 release is a NeoForge file. It is built for Minecraft 1.21.1 and the NeoForge mod loader. Match these requirements when setting up Immersive Engineering Mod.
How to choose the correct file
Check the individual release page rather than relying on a general project badge. Match the Minecraft version to 1.21.1 and verify that your launcher profile uses the compatible NeoForge setup. Consult the release page for any additional installation requirements.
Can 1.20.1 Forge files be reused?
No. The 1.20.1 Forge build is meant for a different game version and a different loader. Downloading a matching release is simpler and safer than attempting to run an incompatible JAR.
Before launching a modpack
When combining Immersive Engineering with another technology mod, make sure every mod is designed for the same game and loader combination. Add mods gradually when troubleshooting so that failures are easier to isolate.
For release-specific details, consult the published Immersive Engineering files before installing or updating your game.