Here is the full log: https://paste.ee/p/sF3Gg

I dont think this is easily fixable due to how things are rendered but i hope it should not be too much of a hassle.

Can confirm this one. Tried with just GeckoLib, just Sodium, and both together in 1.16.3 (even though GeckoLib doesn't officially support 1.16.3), and the crash only shows up when GeckoLib is paired with Sodium. Same log as Matty. I'm gonna guess it has to do with GeckoLib's access widener for renderCuboids(), while Sodium is using @Overwrite on it. Idk how hard that would be to fix since @Overwrite itself is just a pain to do compatibility with.

I do have one idea though: try using an Accessor Mixin instead of an access widener. They can be used on both methods and variables, and should allow you to get access to renderCuboids() without needing an access widener and might maintain some compatibility with Sodium.

This will be fixed in 3.0.0, which is currently in alpha. I have no plans to fix this for 2.0.0 as I don't want people using that anymore after 3.0.0 is fully released so till then I guess it'll have to be broken :/