Minecraft 1.16 is the first major update to Minecraft nether world, it completely overhauls Nether by adding new biomes and mobs, along with a multitude of new blocks, most noticeably Ancient debris.
Here's the full list of blocks that 1.16 update introduced to Minecraft: Ancient debris, Basalt, Blackstone, Block of Netherite, Chain, Chiseled nether bricks, Cracked nether bricks, Crimson and warped fungi, Crimson and warped nylium, Crimson and warped planks, Crimson and warped roots, Crimson and warped stems, Crying obsidian, Gilded blackstone, Hyphae, Lodestone, Nether gold ore, Nether sprouts, Quartz bricks, Respawn anchor, Shroomlight, Soul campfire, Soul fire, Soul lantern, Soul torch, Soul soil, Target, Twisting vines, Warped wart block and Weeping vines.
New Minecraft 1.16 items include Lodestone compass, Music discs, Netherite armor, Netherite tools, Netherite ingot, Netherite scrap, Snout banner pattern, new Spawn eggs and Warped fungus on a stick.
Since this update brought a lot of changes to nether, you will be able to find new mobs there, Hoglins, Piglins, Striders and Zoglins.
There were also a lot of Minecraft bug fixes and general improvements, but it's probably safe to assume most of players will be looking forward to new Netherite tools and armors, which are for now pretty hard to obtain. Netherite tools and armors in Minecraft 1.16 can be crafted from Netherite ingot and for that you will have to find Block of Netherite, which can only be found in Nether, chances of you stumbling over Netherite are even lower than chances of you finding Diamond ore, interesting twist.