As always, I have a problem of a somewhat esoteric and technical nature. :P
I downloaded a theme park map for my kids to have fun on. The whole thing had been generated ultraflat, with a build height set at y=100. I wanted the world gen OUTSIDE the main theme park build area to be 1.20.1 normal overworld generation.
So, I managed to get all the chunks around the main area deleted in MCA Selector and outright removed all superfluous regions, then deleted level.dat to force the game to make new chunks based on default parameters. This worked really, really well - everything outside the theme park is totally great and the biome blending I have to say is pretty exceptional, given two major caveats.
First, most of the theme park would have been mostly in an ocean, and given that the base build height was set to y=100, biome blending is producing a very clear terraced stair-step effect all the way around. That's not a HUGE deal, but I would very much like to drag the base height down to y=64 if that's possible and bring all the content down with it, and retry the biome blending.
Second, because the chunks were generated with zero underground features, all chunks below the builds are dirt down to y=0, and then nothing (no deepslate / bedrock / etc) until you hit the edges where new chunks are made. This is problematic for obvious reasons. Bedrock would be OK, caves would be better, but I'm not sure why it's completely empty. My old worlds that I updated all the way through versions generated deepslate to bedrock from y=-64 to y=0.
Worst case scenario i can just get over the terrace problem, and use worldedit to fill in a bedrock layer and a bunch of deepslate, but I'd rather something more natural for my kids to destroy. :)
Looking for thoughts on this.