biome_modifier:

{
  "type": "minecraft:add_features",
  "biomes": "#minecraft:is_forest",
  "features": [
    "wildgrowth:patch_leaf_litter"
  ]
}

placed_feature:

{
  "feature": "wildgrowth:patch_leaf_litter",
  "placement": [
    {
      "type": "minecraft:block_predicate_filter",
      "predicate": {
        "type": "minecraft:would_survive",
        "block": "wildgrowth:leaf_litter"
      }
    }
  ]
}

configured_feature:

{
  "type": "minecraft:random_patch",
  "config": {
    "feature": {
      "type": "minecraft:simple_block",
      "config": {
        "to_place": {
          "type": "minecraft:weighted_state_provider",
          "entries": [
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "north", "leaf_amount": "1" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "east", "leaf_amount": "1" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "south", "leaf_amount": "1" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "west", "leaf_amount": "1" } }, "weight": 1 },

            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "north", "leaf_amount": "2" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "east", "leaf_amount": "2" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "south", "leaf_amount": "2" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "west", "leaf_amount": "2" } }, "weight": 1 },

            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "north", "leaf_amount": "3" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "east", "leaf_amount": "3" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "south", "leaf_amount": "3" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "west", "leaf_amount": "3" } }, "weight": 1 },

            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "north", "leaf_amount": "4" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "east", "leaf_amount": "4" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "south", "leaf_amount": "4" } }, "weight": 1 },
            { "data": { "Name": "wildgrowth:leaf_litter", "Properties": { "facing": "west", "leaf_amount": "4" } }, "weight": 1 }
          ]
        }
      }
    },
    "tries": 96,
    "xz_spread": 4,
    "y_spread": 2,
    "placement": [
      {
        "type": "minecraft:block_predicate_filter",
        "predicate": {
          "type": "minecraft:matching_blocks",
          "blocks": ["minecraft:air"]
        }
      }
    ]
  }
}