Minecraft wiki entry for Parity_issue_list, associated text: Mineshafts are much more frequent.
64-bit world seed numbers are used by default.‌[upcoming: BE 1.18.30]
Spikes in basalt deltas are larger and more frequent.[162]
Bastion loot chests frequently generate with gilded blackstone underneath.[163]
Dripstone caves temperatures are warmer.
Igloos always generate with a villager without profession (will see brewing stand or cauldron, and pick a career).
Jungle pyramids can generate in bamboo jungles.
Jungles and old growth taigas have more frequent and denser tree generation.
Nether (crimson and warped) forests are much denser than in Bedrock Edition.
Crimson and warped fungi can generate in small quantities in their counterpart biomes (i.e., crimson fungi in warped forests).[164]
Oak and spruce trees can generate in windswept hills and windswept gravelly hills.
Oak trees can generate in snowy tundras.
Azalea trees can generate with more tree shape and size variant.[165]
Plains are weighted only 1 in warm biome generation instead of 3 ({FOREST, DARK_FOREST, MOUNTAINS, PLAINS, BIRCH_FOREST, SWAMP} instead of {FOREST, DARK_FOREST, MOUNTAINS, PLAINS, PLAINS, PLAINS, BIRCH_FOREST, SWAMP}).
Red sandstone can generate in badlands and eroded badlands.
Savannas and plains generate a lot more grass.
Solid terrain, structures, and biome generation can generate all the way to 2.147 billion blocks (if the hardcoded 30 million block limit is removed).
Strongholds always generate end portals.[166]
Villages can spawn in superflat.
World boundary exists at the edge of the world.