first of all i tried this,
{
"config_version": {
"id": "99",
"version": 0
},
"dimensions": [
{
"dimensiontype": {
"id": 99,
"name": "initialstart2",
"worldprovider": "WorldProviderSurfaceJED",
"biome": "minecraft:forest",
},
"worldinfo_onetime": {
"generatorOptions": "3;minecraft:bedrock,64minecraft:stone,6minecraft:sandstone,6*minecraft:sand,lake,lava_lake",
},
}
]
}
and set in jedconfig to be the initialworldspawn. it create the worlds but the configs doesnt aplyes so, i dunnok.
AM Trying to do a single biome dimensions with water lakes, and some sand stone, etc blocks, but without caves and nothing else thana defult forest biome but not flat.

This was answered in CurseForge comments.