I'll try to explain what the experimental features in quark do.
Adjustable Chat:
Moves the chat screen in game, you can adjust the horizontal and vertical shift.
Image shows the chat shifted by 11.
Spawner Replacer:
Replaces the mobs in spawners, for example it can replace spider spawners with creepers spawners.
Narrator Readout:
Adds 2 keybinds, 1 triggers the narrator to narrate what you're looking at, the other makes it narrate what you're looking, your health, armor, what you're holding.
demo of this on twitter
Game Nerfs:
Personal favorite, it adds various nerfs to Minecraft. All of the nerfs are explained in the config & Q button.
Nerf Mending: Makes Mending act like the Unmending mod.
Nerf Villager Discount: Resets all villager discounts when zombified to prevent reducing prices to ridiculous levels.
Disable Iron Farms: Makes Iron Golems not drop Iron Ingots.
Disable Ice Roads: Makes Boats not glide on ice.
Disable Wool Drops: Makes Sheep not drop Wool when killed.
Enable Selective Mob Griefing: Disables mob griefing for only specific entities.
Enable Dimension Locked Elytra: Force Elytra to only work in specific dimensions.
Disable Falling Block Dupe: Makes falling blocks not able to be duped via dimension crossing.
Disable Piston Physics Exploits: Fixes several piston physics exploits, most notably including TNT duping.
Enchantments Begone:
Removes specific enchantments to generate in book form on chest and villager trades and also to not appear on the enchanting table.
Enchantment Predicates:
It's explained in the config & Q button, very technical.
This feature generates Resource Pack Item Model predicates on the items defined in 'Items to Change' for the Enchantments defined in 'Enchantments to Register'.
Overlay Shader:
It's explained in the config & Q button.
Sets the name of the shader to load on a regular basis. This can load any shader the Camera module can (and requires the Camera module enabled to apply said logic).