Here is a list of superflat presets that I like to use

Here is a preset for the Redstone Ready world type to use grass as the top layer, and be a plains biome Well, this one only creates it with grass for 116 layers, I will change it to be dirt and stone for some layers. minecraft:bedrock,3minecraft:stone,116minecraft:grass_block;minecraft:plains

Here is a good website to generate flat world presets: https://minecraft.tools/en/flat.php

List of presets generated from that site:

1 grass layer, 30 layers of dirt, 30 layers of stone, and 3 layers of bedrock

3minecraft:bedrock,30minecraft:stone,30*minecraft:dirt,minecraft:grass_block;minecraft:plains;village