Using MCA Selector im compiling lots of previous builds from old worlds into one world by copy-pasting chunks into a new world. The chunk blending works for all chunks from older versions, but does not work apropriately from chunks that were generated in 1.20 which results in chunk borders.

Att1: chunk not blending when sorounded by 1.20 chunks
Att2: Left: 1.17 terrain blending with no issue; right: 1.20 terrain not blending
Att3: Left: 1.18 terrain blending ; right 1.20 terrain not blending