I'm facing a strange issue with custom biomes in Forge 1.18. Essentially they do not seem to be generated or be registered at all...

This is how I'm registering a biome
 

@Mod.EventBusSubscriber(modid = "test", bus = Mod.EventBusSubscriber.Bus.MOD)
public class CommonModEvents {

    @SubscribeEvent
    public static void registerOres(FMLCommonSetupEvent event) {
        event.enqueueWork(BiomeGeneration::registerBiomes);
    }
}

public class BiomeGeneration {

    public static final ResourceKey<Biome> TEST_BIOME = ResourceKey.create(Registry.BIOME_REGISTRY, new ResourceLocation("test", "test_biome"));

    public static void registerBiomes() {
        BiomeDictionary.addTypes(TEST_BIOME, BiomeDictionary.Type.FOREST);
        BiomeManager.addAdditionalOverworldBiomes(TEST_BIOME);
    }
}

And this is the Biome json file. Nothing crazy here, just a Birch Forest json file without Birch trees (just to see if it actually spawns)
 

{
  "effects": {
    "mood_sound": {
      "sound": "minecraft:ambient.cave",
      "tick_delay": 6000,
      "block_search_extent": 8,
      "offset": 2.0
    },
    "sky_color": 8037887,
    "fog_color": 12638463,
    "water_color": 4159204,
    "water_fog_color": 329011
  },
  "carvers": {
    "air": [
      "minecraft:cave",
      "minecraft:cave_extra_underground",
      "minecraft:canyon"
    ]
  },
  "features": [
    [],
    [
      "minecraft:lake_lava_underground",
      "minecraft:lake_lava_surface"
    ],
    [
      "minecraft:amethyst_geode"
    ],
    [
      "minecraft:monster_room",
      "minecraft:monster_room_deep"
    ],
    [],
    [],
    [
      "minecraft:ore_dirt",
      "minecraft:ore_gravel",
      "minecraft:ore_granite_upper",
      "minecraft:ore_granite_lower",
      "minecraft:ore_diorite_upper",
      "minecraft:ore_diorite_lower",
      "minecraft:ore_andesite_upper",
      "minecraft:ore_andesite_lower",
      "minecraft:ore_tuff",
      "minecraft:ore_coal_upper",
      "minecraft:ore_coal_lower",
      "minecraft:ore_iron_upper",
      "minecraft:ore_iron_middle",
      "minecraft:ore_iron_small",
      "minecraft:ore_gold",
      "minecraft:ore_gold_lower",
      "minecraft:ore_redstone",
      "minecraft:ore_redstone_lower",
      "minecraft:ore_diamond",
      "minecraft:ore_diamond_large",
      "minecraft:ore_diamond_buried",
      "minecraft:ore_lapis",
      "minecraft:ore_lapis_buried",
      "minecraft:ore_copper",
      "minecraft:underwater_magma",
      "minecraft:disk_sand",
      "minecraft:disk_clay",
      "minecraft:disk_gravel"
    ],
    [],
    [
      "minecraft:spring_water",
      "minecraft:spring_lava"
    ],
    [
      "minecraft:glow_lichen",
      "minecraft:forest_flowers",
      "minecraft:flower_default",
      "minecraft:patch_grass_forest",
      "minecraft:brown_mushroom_normal",
      "minecraft:red_mushroom_normal",
      "minecraft:patch_sugar_cane",
      "minecraft:patch_pumpkin"
    ],
    [
      "minecraft:freeze_top_layer"
    ]
  ],
  "spawners": {
    "monster": [
      {
        "type": "minecraft:spider",
        "weight": 100,
        "minCount": 4,
        "maxCount": 4
      },
      {
        "type": "minecraft:zombie",
        "weight": 95,
        "minCount": 4,
        "maxCount": 4
      },
      {
        "type": "minecraft:zombie_villager",
        "weight": 5,
        "minCount": 1,
        "maxCount": 1
      },
      {
        "type": "minecraft:skeleton",
        "weight": 100,
        "minCount": 4,
        "maxCount": 4
      },
      {
        "type": "minecraft:creeper",
        "weight": 100,
        "minCount": 4,
        "maxCount": 4
      },
      {
        "type": "minecraft:slime",
        "weight": 100,
        "minCount": 4,
        "maxCount": 4
      },
      {
        "type": "minecraft:enderman",
        "weight": 10,
        "minCount": 1,
        "maxCount": 4
      },
      {
        "type": "minecraft:witch",
        "weight": 5,
        "minCount": 1,
        "maxCount": 1
      }
    ],
    "creature": [
      {
        "type": "minecraft:sheep",
        "weight": 12,
        "minCount": 4,
        "maxCount": 4
      },
      {
        "type": "minecraft:pig",
        "weight": 10,
        "minCount": 4,
        "maxCount": 4
      },
      {
        "type": "minecraft:chicken",
        "weight": 10,
        "minCount": 4,
        "maxCount": 4
      },
      {
        "type": "minecraft:cow",
        "weight": 8,
        "minCount": 4,
        "maxCount": 4
      }
    ],
    "ambient": [
      {
        "type": "minecraft:bat",
        "weight": 10,
        "minCount": 8,
        "maxCount": 8
      }
    ],
    "axolotls": [],
    "underground_water_creature": [
      {
        "type": "minecraft:glow_squid",
        "weight": 10,
        "minCount": 4,
        "maxCount": 6
      }
    ],
    "water_creature": [],
    "water_ambient": [],
    "misc": []
  },
  "spawn_costs": {},
  "precipitation": "rain",
  "temperature": 0.6,
  "downfall": 0.6,
  "category": "forest"
}

If I try to locate the biome using the /locatebiome test:test_biome it says that it can't find the Biome. Also, if I try to generate a single biome world, the custom biome doesn't even show in the biomes list. What I noticed, in comparison to 1.17, is that the BiomeEntry class essentially is ignoring the weight parameter. This is the 1.17 BiomeEntry class
 

public static class BiomeEntry extends WeighedRandom.WeighedRandomItem
    {
        private final ResourceKey<Biome> key;

        public BiomeEntry(ResourceKey<Biome> key, int weight)
        {
            super(weight);
            this.key = key;
        }

        public ResourceKey<Biome> getKey()
        {
            return this.key;
        }
    }

And this is the 1.18 one
 

public static class BiomeEntry
    {
        private final ResourceKey<Biome> key;

        public BiomeEntry(ResourceKey<Biome> key, int weight)
        {
            this.key = key;
        }

        public ResourceKey<Biome> getKey()
        {
            return this.key;
        }
    }

Also, looking at the BiomeManager class, specifically the getAdditionalOverworldBiomes method, which should be used to attach the mod biomes to the vanilla ones, if you try to look for method usages, in 1.18 it appears that this method is unused. This is what IntelliJ shows if I run the "Find usages" command on this method
https://imgur.com/a/r0Fvkjp

Where in 1.17 this method is called by the OverworldBiomeSource constructor to attach the mod biomes to the already registered ones
 

public OverworldBiomeSource(long p_48590_, boolean p_48591_, boolean p_48592_, Registry<Biome> p_48593_) {
      super(java.util.stream.Stream.concat(POSSIBLE_BIOMES.stream(), net.minecraftforge.common.BiomeManager.getAdditionalOverworldBiomes().stream()).map((p_48603_) -> {
         return () -> {
            return p_48593_.getOrThrow(p_48603_);
         };
      }));
      //...
   }

So, am I missing something during the creation of a Biome in 1.18 or there's still something missing on this?

this is at the moment not implemented, since vanilla changed the Biome generation, and the old Forge patch doesn't work anymore
you need to wait till it's will be added back