Source: Java Edition 1.18 – Minecraft Wiki
-Added Otherside music disc by Lena Raine
-Changed caves and cliffs generations
-Stretched the y level -64 to 319
-Added biomes:
Meadow, Grove, Snowy Slopes, Jagged peaks, frozen peaks, stony peaks
-Added command format /jfr
-Added advancements:
Caved and cliffs, Feels like home, Sound of music, Star trade
-Added illageralt font
-Added languages:
Lombard, Tokipona
-Added Songs:
By Lena Raine:
Stand Tall, Left to Bloom, One More Day, Wending, Infinite Amethyst
By Kumi Tanioka:
Floating Dream, Comforting Memories, An Ordinary Day
-Added Simulator Distance setting
-Added Allow server listings setting
-Changed Textures:
Anvil GUI, Carrot, Cartography table, Cave vines, Cocoa beans, Dirt path, Enchanting table GUI, Glass pane, Lectern, Logs, Comparator, Blue and red stained glass, Beetroot seeds, melon seeds, campfire, soul campfire, Doors, Item frame and glow item frame
-Axolotls can only spawn in lush caves with clay blocks as the floor
-Cod, salmon, pufferfish, tropical fish, squid, dolphins cam only spawn in y=50 to y=64
-Goats spawn only in snowy slopes, jagged peaks, and frozen peaks
-Geodes only generate up to y=30
-Changed biome names:

Old name	New name
Tall Birch Forest	Old Growth Birch Forest
Giant Tree Taiga	Old Growth Pine Taiga
Giant Spruce Taiga	Old Growth Spruce Taiga
Snowy Tundra	Snowy Plains
Jungle Edge	Sparse Jungle
Stone Shore	Stony Shore
Mountains	Windswept Hills
Wooded Mountains	Windswept Forest
Gravelly Mountains	Windswept Gravelly Hills
Shattered Savanna	Windswept Savanna
Wooded Badlands Plateau	Wooded Badlands

-Removed Biomes:

Badlands Plateau

Bamboo Jungle Hills

Birch Forest Hills

Dark Forest Hills

Deep Warm Ocean

Desert Hills

Desert Lakes

Giant Spruce Taiga Hills

Giant Tree Taiga Hills

Gravelly Mountains+

Jungle Hills

Modified Badlands Plateau

Modified Jungle

Modified Jungle Edge

Modified Wooded Badlands Plateau

Mountain Edge

Mushroom Field Shore

Shattered Savanna Plateau

Snowy Mountains

Snowy Taiga Hills

Snowy Taiga Mountains

Swamp Hills

Taiga Hills

Taiga Mountains

Tall Birch Hills

Wooded Hills

-Buried treasures can contain water breathing potions
-Changed ore distribution
-Fixed 240 Glitches

Let me know if I missed some