Nullshard is a minor update to the existing End biomes without adding any additional ones, inspired by the biomes seen in Minecraft Dungeons' "Echoing Void" DLC. It also updates the End Ship, and I plan to update the rest of the End City at some point too.
The namesake of this mod, the "Nullshard Crystal", is a new ore found in the End that serves as an alternative to Netherite- not an upgrade to it. All Nullshard items will float in the air, meaning you probably won't lose them if you die in the void.
Probably.

To upgrade your gear to Nullshard, you need a Nullshard Upgrade Smithing Template. These can rarely be found in End City loot chests, and can be duplicated with Echo Shards and Obsidian.

While the armor lacks knockback resistance, it has a special effect where it reduces the effects of Levitation and Slow Falling, with each armor piece worn increasing that effect such that a full armor set makes you effectively immune to Levitation.
The tools have nothing special about them, they're just there to look pretty.

Chorus plants now drop Chorus Stalk when broken instead of Chorus Fruit, a new wood that can be crafted into magenta Chorus Planks. Chorus Flowers now only drop themselves when broken with Silk Touch, otherwise they drop Chorus Buds. Chorus Buds drop Chorus Fruit when broken without Silk Touch. If there is a 12-block gap of air between Chorus Buds and an Endstone block below it, there is a chance for the Chorus Bud to drop a Chorus Flower into the world.

Unakite is a new stone type that typically generates near pools of Acid, or more rarely Water. It can be used to craft the same things that use the tags "stone_tool_materials" and "stone_crafting_materials", as well as into its own blocksets.
Acid is a new fluid that poisons and harms any entity that touches it. This is data-driven, so if you'd like to make an entity immune to acid you can add them to the "nullshard:acid_immune" entity tag.

Nullshard (End Update)