• Create a buffet world (type floating island) with generate structures OFF
• edit level.dat to make it a void world with vanilla biomes (generatorOptions > biome_source: type: minecraft:vanilla_layered // chunk_generator: > options: default_block: minecraft:air + default_fluid: minecraft:air)
• delete "region" folder in saves

As seen on the screenshot there are still bone fossils and it seems there is no way to disable them