Installation is straightforward when all three parts match: Minecraft 1.21.1, a compatible NeoForge 21.1 loader, and the 12.4.2-194 Immersive Engineering JAR.
Step 1: prepare a clean game profile
Create or choose a Minecraft 1.21.1 profile. If you use a multi-instance launcher, note the exact instance folder because it may not use the global Minecraft directory.
Step 2: install a compatible NeoForge build
The included JAR declares NeoForge 21.1.164 or newer as required. Use a loader version that is intended for Minecraft 1.21.1 and is compatible with the rest of your modpack.
Step 3: copy the mod into the correct folder
Place the JAR in the mods folder for that instance. Do not extract the JAR, rename it as an APK, or put it into a resourcepacks folder.
Step 4: verify the first launch
Start the profile and check the loaded mod list. Create a temporary test world or use a backup before committing an important save to a changed mod list.
Next step
Once your setup is stable, use the other guides on this site to plan power, wiring, performance and larger factory systems. For the file itself, use the main direct download section on the homepage.