1. Match Minecraft and the loader before getting the JAR
The checked Java project is Verity JE by VarmiteYT, CurseForge Project ID 1591438. Checked July 18, 2026, its files include a Forge branch for Minecraft 1.20.1 and an older NeoForge branch for Minecraft 1.21.1. The project page describes the NeoForge 1.21.1 branch as deprecated and buggy, so a larger game-version number is not automatically the better choice. Read the current files page and changelog before selecting.
Create a separate launcher profile for the exact Minecraft version. Install the corresponding Forge or NeoForge loader from its own official source, then launch that profile once before adding Verity. The first launch proves that Minecraft, Java, and the loader work together and creates the profile folders. Close the game after reaching the menu. If the loader itself fails, fix that before introducing the mod.