Choonster

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Can you reproduce this on 1.21.11-61.0.8? And definitely not in Vanilla? If so, I'd recommend reporting it on GitHub, making sure to provide all the information requested in the issue template.

m_6631_ is Tier.getAttackDamageBonus, you can see the call in the Basic Weapons code here. I'm not sure why this is happening, the fg.deobf call in build.gradle should be deobfuscating the dependency from SRG to Official/Parchment names. Did you definitely have fg.deobf in place when you got this crash? Try refreshing the Gradle project in your IDE to make sure it's in sync with the build script. In IntelliJ IDEA, this can be done with the "Sync All Gradle Projects" button in the Gradle window. If this doesn't help, you may want to ask in the #mod-dev-support-1․20․x channel on Discord as there are people there that don't read the forums.

Your repository appears to be private. You probably need to add the MixinGradle plugin to allow it to deobfuscate the mixins from your dependency. You shouldn't need the annotation processor or other configuration from that page unless you're using mixins yourself.

The SwordItem class doesn't exist in newer versions, Mojang moved the sword functionality to Data Components. Look at the sword registrations in the Items class for examples of this.

Forge for 1.21.6 and newer uses EventBus 7, which is a major rewrite. You can read the migration guide here, this explains how to cancel events.

Rubidium and Embeddium are versions of the same mod, you can only have one. I believe Embeddium is the one that's actively maintained.

Can you reproduce this with version 55.0.21? A whole lot of plant placement issues were just fixed in this PR.

Yes, once you have data generation set up, it's a lot easier to add a line of code to your generator class than it is to copy, paste and edit 2-3 JSON files for each new item.

Minecraft 1.21.4 requires a new model definition file for each item, which you don't have. These can be created through Data Generation, specifically the ModelProvider, BlockModelGenerators and ItemModelGenerators classes.

https://forums.minecraftforge.net/topic/155182-trying-to-play-1201-in-multimc-with-forge-mods-but-this-error-all-the-time/

You can try their Ideas Portal, linked from the footer of their site.

You seem to be confusing Minecraft Forge (a mod loader, this site) with CurseForge (a mod distribution platform for Minecraft and other games). The two are unrelated, you probably want to take this feedback to CurseForge.