My code: 

@SubscribeEvent
	public static void addFeaturesToBiomes(BiomeLoadingEvent event) {
		for (FeatureRegistration registration : FEATURE_REGISTRATIONS) {
			if (registration.biomes() == null || registration.biomes().contains(event.getName()))
				event.getGeneration().getFeatures(registration.stage()).add(registration.placedFeature().get());
		}
	}

At BiomeLoadingEvent I get the following error:

BiomeLoadingEvent cannot be resolved to a type

-----------------------------------------

Imports:

import net.minecraftforge.event.world.BiomeLoadingEvent;

And in the imports I also get an error:

The import net.minecraftforge.event.world.BiomeLoadingEvent cannot be resolved

It would be great if you could help me. 🙂

Unfortunately I didn't worked with 1.19 yet. But it looks like the BiomeLoadingEvent has been removed. Unfortunately I'm not be able to told you what the replacement is since I'm not familiar with 1.19 code. 

It's changed quite a bit. Fortunately, a youtuber, Kaupenjoe, has an explanation in his updating 1.18.2 to 1.19 video how to get feature generation into your 1.19 worlds, but there seems to still be some issues where a world won't load after creating it the first time.

https://forge.gemwire.uk/wiki/Biome_Modifiers