Running Minecraft 1.21.0 with Fabric Loader 0.16.9 and Fabric API 0.102.0 , running either NoClip 1.3.1 or Head Index 1.1.8 alone has no errors at all, but running both together causes a crash both on my PC and on my Aternos server. The first error thrown says that it's from sgui (part of Head Index) but the crash log says that NoClip caused the crash, so I am posting this in both places to try to get further clarity.

Full Log:
https://paste.ee/p/2wQ08

Appears to be a problem with a version mismatch, see the other issue for more details.