FOSS gamedev and creative worlds

When I genarate a world, it looked like the dirt and trees and rivers have been ripped off the landscape. there is only stone and minerals underground. I used V7 gen which made it completely barren, but my V6 gen leaves some biomes but is still mostly barren. I used no mods.

You can not change map gen on an existing world, if that is what you tried,

v7 is not recommended yet, and needs mods to add content.
v6 is the current standard: it should generate grass, desert, cliffs, trees, seas, lakes, dungeons, minerals etc.