A world with nothing in it, literally! Not even a starting platform or block. Just the default settings, without structures generating, void superflat world preset. Pure void.
I had looked up to see if there was any maps that someone made that had literally nothing in it. Turns out the only ones that I found were void worlds that had a single block or platform, or even a base. That is why I had made this so players can use datapacks to create some their own worldgen without using the worldgen. I tried to make it like you had completely nothing, no changes to the world, default time. But I couldn't make it perfect, and I also fell off the world, so time would be a little bit more than expected and you would also have to respawn once you open the world because you were dead.
If there is a way to add packs from a folder to a world, without mods, I would make it into a datapack.