Summary:

Deepslate transition ceilings in pre-1.19 worlds when upgraded to 1.19 and above have noticeably flat ceilings especially when seen on big caves. Unlike in Java Edition, it tries to hide the imperfection by adding more terrain or "blending" it to make the ceiling naturally "seamless" and not just a flat ceiling.

Steps to reproduce:

1. Have a world created below 1.17
2. Then open that world in 1.20 and go to the deepslate layers

Observed results:

Deepslate caves on old chunks more specifically the big ones, will have the noticeable flat deepslate transition ceiling.

Expected results:

Deepslate caves in old chunks more specifically the big ones, should have not so easily noticeable deepslate transition ceiling and not just a flat ceiling.

Images:

Bedrock 1.20.41

Java 1.20.2

Sample World: https://drive.google.com/drive/folders/11snUoHC1KVQl6yNzXruwqoULhWOF2iDI?usp=sharing

1. Download the world "SampleWorld_Bedrock", then open that world in Minecraft Bedrock 1.17, teleport to the coordinates 5023 -9 -171, and you should teleport to the void below the bedrock ceiling because the world hasn't been updated yet to the new Caves and Cliffs world generation.
2. Open the same world but in Bedrock 1.19 and above (or you can choose 1.20), upgrade the world, teleport to the same coordinates, and it should have been upgraded to the new Caves and Cliffs world generation where the new deepslate caves generate below the old chunks and you should see the notable flat deepslate ceiling that used to be bedrock.
3. Try to compare that world to "SampleWorld_Java", download and open the world in Minecraft Java 1.20, teleport to the same coordinates "5023 -9 -171", and you should see that the blending algorithm in Java tries to "hide" the flat deepslate ceiling imperfection by adding more blocks to blend the old ceiling to the new deepslate cave walls.