Coal ore, iron ore, gold ore, and redstone ore had the shape of the "ore pattern" in the stone changed to make them visually distinct for colorblind players.
Diamond ore remains mostly the same as it was the most iconic one of the ores that used this shape.
Changed ore generation of all ores making them have a spread value and generate in a triangle distribution[2] like lapis lazuli ore. Some still retain a linear generation alongside a spread generation.
Copper ore generates between the Y=0 and Y=96 and like all other ores, uses spread. It peaks at Y=48.
Emerald ore generates above Y=32 (up to Y=480 in custom worlds) as a spread, peaking at Y=256 and decreasing in quantity as the altitude decreases.
Coal ore attempts to generate twice: once, evenly between an altitude of Y=136 and Y=256; and as a spread, peaking at an altitude of Y=96 and generating between an altitude of Y=0 and Y=192.
Other ores also generate differently.
Iron ore attempts to generate twice: once as a spread peaking at an altitude of Y=256, generating above Y=128 (up to Y=384 in custom worlds); and another as a spread peaking at Y=32 and generating with a minimum height of Y=-16 and a maximum height of Y=80.
Gold ore generates between the altitudes of Y=-64 and Y=32, peaking at Y=-16. The extra gold that generates in the badlands biome was left untouched.
Lapis lazuli ore attempts to generate twice: once, as a spread between the altitudes of Y=32 and Y=-32, peaking at an altitude of 0; and evenly between an altitude of Y=64 and Y=-64, generating buried like ancient debris.
Redstone ore attempts to generate twice: once, evenly between an altitude of Y=15 and Y=-64; and as a spread, peaking at an altitude of -64 and generating below an altitude of Y=-32 (down to Y=-96 in custom worlds).
Diamond ore now generate as a spread, generating below Y=16 and peaking at altitudes near Y=-64.
Are now encased in stone and/or grimstone, depending on the depth.
General
Creative inventory
The "Redstone Tab" has been reordered to prioritize highly-used blocks.
Redstone items/blocks have been grouped and ordered in the following way (from top to bottom): Essentials, Unique activators, Miscellaneous, Common activators, Openables.
Data packs
Vanilla configured features for ore types have changed:
Coal and iron have been split into two parts called _upper and _lower.
New lapis configured feature: ore_lapis_buried.
The glow_lichen feature now lists grimstone as a valid block.
Changes to the range decorator configuration:
bottom_offset, top_offset and maximum fields removed.
Replaced with bottom_inclusive and top_inclusive which are both a new type of vertical anchoring.
This type can have several forms:
absolute - specifies an absolute Y value.
above_bottom - specifies an offset above the minimum Y coordinate of the world.
below_top - specifies an offset below the maximum Y coordinate of the world.
The range_biased and range_very_biased feature decorator are now called range_biased_to_bottom and range_very_biased_to_bottom respectively.
Both biased types of ranges now have bottom_inclusive and top_inclusive of the same type, and a cutoff value that's a numeric value
The depth_average decorator also now has its baseline field as a vertical anchor instead of an absolute Y value.
A whole range of decorators no longer exist or have had part of their functionality replaced by using some of the already existing generic decorators:
dark_oak_tree decorator no longer does a heightmap check, needs to be done with a heightmap decorator.
The end_gateway decorator has been split, now used with a combination of chance, square & heightmap - see the end_gateway configuration in the vanilla pack for an example.
The glowstone_blob feature no longer does its own decoration, instead is used with a combination of square & range. See glowstone_extra in vanilla files for example.
The lava_lake feature has also been split, now used with chance, square, and range_biased_to_bottom. See lake_lava for an example.
The water_lake decorator has been removed. Now instead chance, square & range.
The emerald_ore decorator has been removed. Now instead count, square & range.
The fire decorator has been removed. Now instead range, square & count.
The carving_mask no longer has a probability field, replaced with a chance decorator.
MC-125675 – Seagrass placed on the ocean floor can replace ocean monument parts.
MC-147589 – Vines no longer randomly generate in jungles.
MC-183547 – Stone and polished blackstone buttons/pressure plates are located at opposite ends of the spectrum of buttons in the Creative inventory despite being identical in behavior.
From the 1.17 development versions
MC-208613 – Amount of players who need to sleep to skip the night is calculated incorrectly.
MC-208618 – Clicking on a bed immediately skips the night if gamerule playersSleepingPercentage is set to 0.
MC-211224 – Seagrass can occasionally replace parts of a swamp hut.
MC-214082 – Crash after placing soul sand or magma under 2032-block-tall water.
From the previous development version
MC-214814 – Strongholds generate floating and without walls, floors, or ceilings when inside caves.
MC-214885 – Beacon beam only render 256 blocks from source.
MC-214917 – Lapis Lazuli doesn't generate on the lower levels of the world.
MC-214928 – Mineshaft corridor support pillars are made out of wood, not logs.
MC-214973 – Powder snow bucket in a dispenser at Y=319 facing upwards or at Y=-64 facing downwards is replaced with empty bucket, despite no powder snow being placed.
MC-214986 – Large dripstones only generate as stalagmites below Y=0.