So I made a custom hematite ore that I want to spawn inside iron ore. I made a custom Filler Block Type, but when I run the mod, the ore doesn't even generate! Any tips on how to fix this, I keep swearing the code looks right, but maybe there's something minute that I'm missing? Also on 1.16.1 btw, here's the code for reference: 

 

package com.theunknown.andraxxus.world.gen;

import com.theunknown.andraxxus.AndraxxMod;
import com.theunknown.andraxxus.util.RegistryHandler;
import net.minecraft.block.BlockState;
import net.minecraft.block.Blocks;
import net.minecraft.block.pattern.BlockMatcher;
import net.minecraft.world.biome.Biome;
import net.minecraft.world.gen.GenerationStage;
import net.minecraft.world.gen.feature.Feature;
import net.minecraft.world.gen.feature.OreFeatureConfig;
import net.minecraft.world.gen.placement.ConfiguredPlacement;
import net.minecraft.world.gen.placement.CountRangeConfig;
import net.minecraft.world.gen.placement.Placement;
import net.minecraftforge.eventbus.api.SubscribeEvent;
import net.minecraftforge.fml.common.Mod;
import net.minecraftforge.fml.event.lifecycle.FMLLoadCompleteEvent;
import net.minecraftforge.registries.ForgeRegistries;

import static net.minecraft.world.gen.feature.OreFeatureConfig.FillerBlockType.NATURAL_STONE;


@Mod.EventBusSubscriber(modid = AndraxxMod.MOD_ID, bus = Mod.EventBusSubscriber.Bus.MOD)
public class AndraxxOreGen {

    public static  OreFeatureConfig.FillerBlockType END_STONE = OreFeatureConfig.FillerBlockType.create("END_STONE", "end_stone", new BlockMatcher(Blocks.END_STONE));
    public static  OreFeatureConfig.FillerBlockType IRON_ORE = OreFeatureConfig.FillerBlockType.create("IRON_ORE", "iron_ore", new BlockMatcher(Blocks.IRON_ORE));

    @SubscribeEvent
    public static void generateOres(FMLLoadCompleteEvent event) {
        for (Biome biome : ForgeRegistries.BIOMES)   {

            if (biome.getCategory() == Biome.Category.NETHER) {
                genOre(biome, 14, 22, 4, 111, OreFeatureConfig.FillerBlockType.NETHERRACK, RegistryHandler.HEMATITE_BLOCK.get().getDefaultState(), 0);
            } else if (biome.getCategory() == Biome.Category.THEEND) {
                genOre(biome, 14, 22, 4, 111, END_STONE, RegistryHandler.HEMATITE_BLOCK.get().getDefaultState(), 0);
            } else  {
                genOre(biome, 14, 22, 4, 111, IRON_ORE, RegistryHandler.HEMATITE_BLOCK.get().getDefaultState(), 14);

            }
        }
    }
    private static void genOre (Biome biome, int count, int bottomOffset, int topOffset, int max, OreFeatureConfig.FillerBlockType filler, BlockState defaultBlockstate, int size)  {
        CountRangeConfig range = new CountRangeConfig(count, bottomOffset, topOffset, max);
        OreFeatureConfig feature = new OreFeatureConfig(filler, defaultBlockstate, size);
        ConfiguredPlacement config = Placement.COUNT_RANGE.configure(range);
        biome.addFeature(GenerationStage.Decoration.UNDERGROUND_ORES, Feature.ORE.withConfiguration(feature).withPlacement(config));
    }
}

I see that in the previous post you made you have already been told by diesieben07 what the problem is. It seems that you are using the same exact code you posted in the previous post, so you cannot really expect this to work the way you want. You are basically trying to generate your ore inside existing iron clusters, when iron itself hasn't been generated in the world yet! In this case you would need to manually place in the world clusters of iron ore containing inside your custom ore. You could use a Feature to implement that

I completely forgot I posted the code above, that's my bad. Memory failure on my part.

Would I use the same code to generate iron ore before the hematite? I'm still majorly new to modding, so I'm not sure how certain things should be done