This (https://github.com/franiscoder/mostructures/blob/1.16.x/src/main/java/io/github/franiscoder/mostructures/common/init/ModStructures.java#L39) should probably be a mixin to DefaultBiomeFeatures because otherwise modded biomes won't get the feature which will cause it to be cut off on biome borders with modded biomes, make sure you only add the StructureFeature to the correct biomes though.

I think a registry callback event will be better but I'll look into it, thank you!

Psst, I think you might be wrong about this, Half told me that Registry.BIOME covers all of it, but thank you, I'll keep this open for a response and close it in a week.

The issue comes when a mod initializes after yours changing Registry.BIOME.

Yeah, Grunt told me you are right, so I will fix this soon, thank you.

fixed when 0.1.0 comes out