bricklyreal Since you already figured it out, here's the solution for anyone else who may find this thread in the future:
How to use Wurst with NeoForge 1.21.1
- Add the latest Wurst version for Minecraft 1.21.1 to your mods folder (link)
- Don't add Fabric API
- Instead, add the latest Forgified Fabric API for 1.21.1 (link)
- Add Sinytra Connector for 1.21.1 (link)
- Install NeoForge (no need to install Fabric)
Important: If you find older forum posts telling you to downgrade Wurst, Forgified Fabric API, or Sodium, ignore that advice! Those compatibility issues have been fixed and the latest versions work fine now.