Changes were introduced with neoforged/NeoForge@af6cb49 that are incompatible with the current Sodium 0.6.9 release. We need to accommodate the changes and publish a new release.

Log file and crash report from a user who opened a support ticket today.

This only affects Minecraft 1.21.4, since NeoForge is still accepting breaking changes on that version. It does not appear this will be back-ported to earlier versions.

Came here to report this as well, is there a version of NeoForge that can be used without error in the mean time?

Neoforge 21.4.88-beta is the version sodium is currently built against and shouldn't cause any issues. You can see the version we're building against here: https://github.com/CaffeineMC/sodium/blob/dev/buildSrc/src/main/kotlin/BuildConfig.kt#L5

This is now resolved in Sodium 0.6.10.