In the 1.21 Version of Extreme Reactors yellorium_dust no longer exists (See Content Class)

However in your recipe datagen you're still trying to register it as a drop chanche (See Example from your recipe datagen)

This leads to a few KubeJs errors due to missing items. Would it be possible to remove those drop chanches?

Can confirm that I also have this issue, I have Kubsjs, Ex Deorum, and Extreme Reactors for NeoForge 1.12.1 installed.
Error: [23:07:08] [ERROR] ! RegistryAccessContainer.java#150: Failed to read result:item_stack from recipe exdeorum:sieve/dust/golden/yellorium_dust[exdeorum:sieve]: java.util.NoSuchElementException: No value present