A modified version of the Caves & Cliffs preview 2 datapack with smoother terrain, better mountains and increased world height (-64 to 384, 64 blocks higher than the normal preview).
I recommend to allocate 5 or more GB of ram for optimal performance.
If you want the cave biomes I recommend these datapacks:
Deep Dark- https://www.planetminecraft.com/data-pack/deep-dark-concept-datapack-for-minecraft-1-17/
Lush Caves-  https://www.planetminecraft.com/data-pack/lush-caves-5327164/ OR https://www.planetminecraft.com/data-pack/1-17-natural-lush-caves/
Dripstone Caves- https://www.planetminecraft.com/data-pack/dripstone-caves-datapack/