[make modded items appear in dungeon chests (1.16.1)]

I've already registered my item and it show up the the creative inventory fine but I can't get it to spawn in a dungeon

here's my code:

{
  "pools": [
    {
      "rolls": 1,
      "entries": [
        {
          "type": "item",
          "name": "ruby_items:ruby_matter_core",
          "weight": 100
        }
      ]
    }
  ]
}

and the json is in Ruby Items 1.16.1-1.0.0/src/main/recources/data/ruby_items/loot_tables/chests/simple_dungeon.json

was I supposed to write anything in the code? because my class file is empty

package com.mani_cwaf.ruby_items.items;

import com.mani_cwaf.ruby_items.Ruby_Items;
import net.minecraft.item.Item;

public class RubyMatterCore extends Item {
    public RubyMatterCore() {
        super((new Properties().group(Ruby_Items.TAB_RUBY)));
    }
}

 

[Where can I find the method and field unmapped names for 1.16.1]

So my pc got corrupted and a lot of my files where lost, including my mod files. so I redownloaded my mod from curseforge and made a new workspace for it, but now all the class files have unmapped names like func_200947_a and I can tell its supposed to be a sound property because of where it is in my code, but I'm starting to forget some things and I want to be able to translate it. is there a place I can find these functions

[How create and damage a container item]

HOW??

[How to make recipe return an input item]

I am a starter to coding and only started because I wanted to make something for minecraft and thought it wouldn't be too hard, I got my mod working but i want to make a recipe where it makes an item but one of the crafting items stays and doesn't get used up like the buckets when making a cake. I don't know what code to put where and keep getting errors, I hear somewhere that when declaring the item you gave it the container property but it doesn't allow the item name.

package com.mani_cwaf.ruby_items.items;

import com.mani_cwaf.ruby_items.Ruby_Items;
import net.minecraft.item.Item;

public class RubyRefiner extends Item {

    public RubyRefiner() {
        super(new Properties()
                .group(Ruby_Items.TAB_RUBY).maxStackSize(1).containerItem(RubyRefiner));
    }

}

that entry into .containerItem() keeps giving the errror "expression expected", what should I do?

[Creating Tile Entities in 1.16]

I'm new to modding and have never done modding in anything and don't know java and all the tutorials on Youtube and everywhere I could find online are outdated or incomplete and I was left at a tutorial not knowing how to make a custom furnace I wanted to, does anyone have a complete and easy tutorial for modding in 1.16.1 that's free?