Welcome to a biome whitelister for Minecraft 1.19!

TL;DR: How to generate a Minecraft world of only certain biomes.

Or, How to make a Minecraft world of only biomes I want

What this is:

Used to generate a list of biomes and their parameters from a specific set of selected biomes. This can then be pasted into a .json and used in a datapack for Minecraft. It should work for versions 1.16 and up.

Of note: Terrain generation appears to be unaffected as Minecraft first generates terrain and then assigns it a biome. This biome then impacts structure generation, mob spawning, biome color, and other such features.

To change terrain generation, edit the .json files within the noise_settings folder. (see below)

How to use:

Edit file.py such that allow_biomes = ["your biome", "other biome"] contains all the biomes you want allowed. Of note, minecraft:ocean will only allow the ocean biome, while ocean will allow the ocean biome and its variants, such as frozen_ocean, or deep_lukewarm_ocean.
The default file whitelists ocean-like biomes.

Edit file.py such that all_biomes is a multiline string of all the of the default biomes and their parameters. This code works under the assumption that you have a list of all vanilla generation biomes. This list can be found at https://github.com/Arcensoth/mcdata/tree/master/generated/reports/biome_parameters/minecraft

More vanilla world generation can be found at https://github.com/slicedlime/examples

The default file includes the 1.19 biome generation parameters

Once set, simply run whitelist_biomes.py. This will generate the out.json file.

From here, find normal.json within the world_preset folder and edit it such that "preset": "minecraft:overworld" is replaced by the entire contents of out.json.

Save normal.json and launch Minecraft. When creating a new world, add your datapack with these changes to the world. Cycle through the world presets until you come back to Default. Now you can generate the world with your custom biomes as a preset.

Using this as a datapack:

The above assumes you already have a solid grasp of datapacks.
Here we'll go into more detail. A more general tutorial can be found at https://minecraft.fandom.com/wiki/Tutorials/Creating_a_data_pack

Download https://github.com/slicedlime/examples/raw/master/vanilla_worldgen.zip to obtain the default world generation settings. Previous Minecraft versions are available under commits.

Extract this zip to vanilla_worldgen

Create a new folder where you like named mydatapack

Create a new folder within mydatapack named data

Create a new folder within data named minecraft
This will overwrite Minecraft defaults with any edits you make. Because of this, it is recommended that you delete any files you haven't edited.

Copy the worldgen folder from vanilla_worldgen into minecraft

Delete all folders within worldgen except for world_preset

Delete all files within world_preset except for normal.json

Other files and folders can be kept if you wish to edit them instead.
For example, to change the sea level in a world, keep the noise_settings folder and overworld.json. Then find sea_level: 63 and change it to sea_level: 100 to change the default sea level to 100.

Note: sea mob generation is still capped at y 63.

These .json files control the noise settings used under the settings: tag found in the world_preset files. Changes here will impact terrain generation.

Within the normal.json file, after running whitelist_biomes.py, paste the entire contents of out.json over "preset": "minecraft:overworld"

Your normal.json should now look something like below.
Biomes may be repeated several times as they can have different parameters.
The spacing / formatting will look atrocious, but you can auto-style it or leave it as is.

{
"dimensions": {
  "minecraft:overworld": {
    "type": "minecraft:overworld",
    "generator": {
      "type": "minecraft:noise",
      "settings": "minecraft:sealevel_overworld",
      "biome_source": {
        "type": "minecraft:multi_noise",
        "biomes": [
          {
            "biome": "minecraft:lush_caves",
            "parameters": {
              "temperature": [
                -1,
                1
              ],
              "humidity": [
                0.7,
                1
              ],
              "continentalness": [
                -1,
                1
              ],
              "erosion": [
                -1,
                1
              ],
              "weirdness": [
                -1,
                1
              ],
              "depth": [
                0.2,
                0.9
              ],
              "offset": 0
            }
          },
          {
            "biome": "minecraft:deep_dark",
            "parameters": {
              "temperature": [
                -1,
                1
              ],
              "humidity": [
                -1,
                1
              ],
              "continentalness": [
                -1,
                1
              ],
              "erosion": [
                -1,
                -0.375
              ],
              "weirdness": [
                -1,
                1
              ],
              "depth": 1.1,
              "offset": 0
            }
          }
        ]
      }
    }
  },
  "minecraft:the_end": {
    "type": "minecraft:the_end",
    "generator": {
      "type": "minecraft:noise",
      "settings": "minecraft:end",
      "biome_source": {
        "type": "minecraft:the_end"
      }
    }
  },
  "minecraft:the_nether": {
    "type": "minecraft:the_nether",
    "generator": {
      "type": "minecraft:noise",
      "settings": "minecraft:nether",
      "biome_source": {
        "type": "minecraft:multi_noise",
        "preset": "minecraft:nether"
      }
    }
  }
}
}

Of note: If you wish to create multiple dimensions, than can be done here, too.
Simply copy / paste new dimensions or write your own, making sure their names are unique. The settings tag references a .json file within noise_settings. You may modify, rewrite, or create your own settings file.

Return to the mydatapack folder

Here, next to the data folder, create a file named pack.mcmeta

Open pack.mcmeta and paste the following:

{
"pack": {
  "pack_format": 10,
  "description": "I made a datapack!!!"
}
}

You may also create an icon for the pack here in the form of a 128 x 128 pixel image. Save it as pack.png.

I've also included a demo datapack of only ocean-y biomes with an increased sea level, along with some extra dimensions. As per https://minecraft.fandom.com/wiki/Custom_dimension,
"New dimensions added can be accessed currently only by using commands, like /execute in <dimension> run teleport <coordinates>."

After launching Minecraft and preparing to create a world, paste the mydatapack folder into the datapacks subfolder of the world being created. This must be done prior to world generation.

As described before, cycle through the world presets and select Default.
A full cycle must occur, otherwise the true default world generation will be used instead of our modified default.

Final thoughts:

I've also included blacklist_biomes.py to instead exclude listed biomes. The use is still the same as whitelist_biomes.py.

The script is by no means efficient or elegant, but this was the work of an afternoon and I realized the community might want it.

Be sure to check out https://minecraft.fandom.com/wiki/Minecraft_Wiki if you have additional questions. Happy modding!

This tutorial is in no way affiliated with anything