anyone know how to create additional overworld as custom dimension in 1.18?

i tried it with my "old" 1.17 dimension

i was not able to use "type": "minecraft:vanilla_layered", as biome_source and used "type": "minecraft:multi_noise",      "preset": "minecraft:overworld" instead .. but if i go into "not generated" world area, i get following exception: (open attached exception.exe)

from https://misode.github.io/dimension/ i used following code:
{
  "type": "minecraft:overworld",
  "generator": {
    "type": "minecraft:noise",
    "seed": 1597774108234513547,
    "settings": "minecraft:overworld",
    "biome_source":

{       "type": "minecraft:multi_noise",       "preset": "minecraft:overworld"     }

  }
}

instead of older version 

{
  "type": "minecraft:overworld",
  "generator": {
    "type": "minecraft:noise",
    "seed": 1597774108234513547,
    "settings": "minecraft:overworld",
    "biome_source":

{       "type": "minecraft:vanilla_layered",       "seed": 1597774108234513547,       "large_biomes": false     }

  }
}

 

but after placing my 1.17 dimension, i get those exceptions ... here you can see the world-blending iam talking from https://minecraft.fandom.com/wiki/Java_Edition_1.18#General_2 
> Added blending_data containing data to support blending new world generation with existing chunks.

Why do it crash when blending? 
Why are there only "until" and "needs testing" infos on https://minecraft.fandom.com/wiki/Custom_dimension and "awaiting" status on https://misode.github.io/dimension ?

And one more last question: why is end portal on standard generated map with seed 6841401455424705842 buggy melted with an ore?

I will pre-generate a big part of our 1.17 world, so that i can migrate our "old" 1.17 server as custom dimension in new 1.18 world, and hope that you will find a solution for this problem - one day someone will reach the end of pregenerated area, and server will crash cause of "blending error" ..

greetings and thanks - leo