As of about a month ago there’s https://github.com/soapantelope/mindcraft. You can give it a prompt like “A Minecraft world of beautiful flower-filled meadows abruptly changing into swamps.” and get that. As far as I can tell it’s using Minecraft’s existing world generator, the readme notes “As of now, Mindcraft can only generate worlds that are feasible natural overworld biomes in Minecraft 1.21.11. Keep this in mind when thinking of prompts!”.

And I’ve seen people hook up LLMs more directly with some scripting tools to place blocks/spawn entities, they do okay.