This is not my resource pack. But How could I fix it?

The mycelium block has been my most frustrating block.
It's the only block where using the auto-generation system has been the most broken, so I provided actual textures instead.

Currently to fix this you'd need to provide your own textures.
I can look into moving this into the lambdabettergrass/default resource pack starting from 1.19.3 since it'll enable automatically on first installation, solving my original concern.

How would I be able to add textures of the side of the mycelium?

Would the location of the textures have to be located in assets\lambdabettergrass\textures\block\mycelium\?

Ok thanks

There's 3 texture files, representing each possible state:

• mycelium_blend_up.png representing the angle from top left to down right
• mycelium_blend_up_m.png a "mirror" of the previous state, it's basically the inverse, angle from down left to top right
• mycelium_side_arch.png representing the arch that can happen when there's mycelium on both sides

those are indeed located in assets/lambdabettergrass/textures/block/mycelium.
Tho, with 1.19.3 moving that stuff to the built-in resource pack, I'm recommending the inclusion of this JSON file at assets/minecraft/bettergrass/data/mycelium.json

{
  "layers": [
    {
      "textures": {
        "top": "minecraft:block/mycelium_top",
        "side": "minecraft:block/mycelium_side",
        "overrides": {
          "blend_up": "lambdabettergrass:block/mycelium/mycelium_blend_up",
          "blend_up_m": "lambdabettergrass:block/mycelium/mycelium_blend_up_m",
          "arch": "lambdabettergrass:block/mycelium/mycelium_side_arch"
        }
      }
    }
  ]
}

This will ensure future-proofing of the resource pack.

Ok, Thanks so much!