so uh how would i make cube-like terrain (had to repost irritatingly)

so uh, not sure where to put it but, i want to make a datapack that recreates the cube-shaped Terrain from the promo art, but i have no idea how to really do it duo to the fact that most of it is kinda coded to work a certain way, so you change one thing, now you gotta change another (rivers as an example)
Which yea... am not 100% sure how much of that i'd be able to do really...
image below is the kind of terrain i want to try to recreate using a datapack