The mod class
 

package com.Denis.denmod;

import com.Denis.denmod.init.ItemInit;

import net.minecraft.world.item.CreativeModeTab;
import net.minecraft.world.item.ItemStack;
import net.minecraftforge.api.distmarker.Dist;
import net.minecraftforge.api.distmarker.OnlyIn;
import net.minecraftforge.common.MinecraftForge;
import net.minecraftforge.eventbus.api.IEventBus;
import net.minecraftforge.fml.common.Mod;
import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;

@Mod("denmod")

public class Denmod {
    
    
    public static final String MOD_ID = "denmod";
    
    public static final CreativeModeTab denmod_TAB = new CreativeModeTab(MOD_ID) {
        
        @Override
        @OnlyIn(Dist.CLIENT)
        public ItemStack makeIcon() {
            return new ItemStack(ItemInit.RUBY.get());
            
            return new ItemStack(ItemInit.RUBY_INGOT.get());
        }
    };

    public Denmod() {
        IEventBus bus = FMLJavaModLoadingContext.get().getModEventBus();
        
        ItemInit.ITEMS.register(bus);
        
        
        MinecraftForge.EVENT_BUS.register(this);
    }
    
}

Item.Init
 

package com.Denis.denmod.init;

import com.Denis.denmod.Denmod;
import com.google.common.base.Supplier;

import net.minecraft.world.item.Item;
import net.minecraftforge.registries.DeferredRegister;
import net.minecraftforge.registries.ForgeRegistries;
import net.minecraftforge.registries.RegistryObject;

public class ItemInit {
     public static final DeferredRegister<Item> ITEMS = DeferredRegister.create(ForgeRegistries.ITEMS, Denmod.MOD_ID);
     
     
     public static RegistryObject<Item> RUBY = register("ruby", () -> new Item(new Item.Properties().tab(Denmod.denmod_TAB)));
     public static RegistryObject<Item> RUBY_INGOT = register("ruby_ingot", () -> new Item(new Item.Properties().tab(Denmod.denmod_TAB)));
     
     private static <T extends Item> RegistryObject<T>  register(final String name, final Supplier<T> item){
         return ITEMS.register(name , item);
         
     }
     
     
}

 

Edited August 19, 20223 yr by Denis12345

First of all do not use @OnlyIn it's vanilla only.
Second the #makeIcon in your CreativeModeTab will not even compile, you can not have two return statements.

Edit: Please use the code feature of the Forum or a paste side to post code.

Edited August 19, 20223 yr by Luis_ST