I have tried extending the CerativeModTab and Overriding fillItemList()  but that didn't work,  any ideas?

Show what you tried

package com.stevet.yabm7.Init;

import net.minecraft.core.NonNullList;
import net.minecraft.core.Registry;
import net.minecraft.world.item.CreativeModeTab;
import net.minecraft.world.item.Item;
import net.minecraft.world.item.ItemStack;
import net.minecraft.world.level.block.Blocks;

public class ModCreativeModeTab {
	public static final CreativeModeTab SHAPE_TAB = new CreativeModeTab("shapes") {
		@Override
		public ItemStack makeIcon() {
			 return new ItemStack(Blocks.CHEST);
		}
	};
	
	public static final CreativeModeTab SLOPES_TAB = new CreativeModeTab("slopes") {
		@Override
		public ItemStack makeIcon() {
			 return new ItemStack(Blocks.PEONY);
		}
	};
	
	public static final CreativeModeTab MODBLOCK_TAB = new CreativeModeTab("mbLocks") {
		@Override
		public ItemStack makeIcon() {
			 return new ItemStack(Blocks.TNT);
		}
	};
	

@Override
	   public void fillItemList(NonNullList<ItemStack> p_40778_) {
		      for(Item item : Registry.ITEM) {
		         item.fillItemCategory(this, p_40778_);	
		      }
	   }


	
//@Override
//public void fillItemList(NonNullList<ItemStack> items) {
	
	// copy items
	//NonNullList<ItemStack> tmpItems = items;
	
	// fill the tmpItems
    //for(Item it : Registry.ITEM) {
    //	it.fillItemCategory(this, tmpItems);
    //}
    
    // sort the tmpItems 
    //Collections.sort(tmpItems, new SortByReg()); 

    // fill the items
//    items = tmpItems;
//}


}

first problem is fillItemList()  errors on the @Override ,  but is an exact copy of the CreativeModeTab.class

public final class ModItemTabs extends CreativeModeTab{
	
	  // public ItemStack iconItemStack;
	
	public ModItemTabs(int p_40773_, String p_40774_) {
		super(p_40773_, p_40774_);
	}
			

	
	public static final CreativeModeTab TAB_SHAPES = new CreativeModeTab("shapes") {
		@Override
		public ItemStack makeIcon() {
			 return new ItemStack(Blocks.CHEST);
		}
	};
	      
	public static final CreativeModeTab TAB_MODBLOCK= new CreativeModeTab("mbLocks") {
		@Override
		public ItemStack makeIcon() {
			 return new ItemStack(Blocks.TNT);
		}
	};
	 
		public static final CreativeModeTab TAB_SLOPES = new CreativeModeTab("slopes") {
			@Override
			public ItemStack makeIcon() {
				 return new ItemStack(Blocks.PEONY);
			}
		};
	 

	@Override
	public ItemStack makeIcon() {
		return null;
	}

	// class to sort the Itemstack
	public  static final class SortByReg implements Comparator<ItemStack>
	{
		@Override
		public int compare(ItemStack o1, ItemStack o2) {
			return o1.getItem().getRegistryName().compareTo(o2.getItem().getRegistryName());

		}
	}
	
	/*
	@Override
	   public ItemStack getIconItem() {
		      if (this.iconItemStack.isEmpty()) {
		         this.iconItemStack = this.makeIcon();
		      }

		      return this.iconItemStack;
		   }
*/	
	  // public void fillItemList(NonNullList<ItemStack> p_40778_) {
		//      for(Item item : Registry.ITEM) {
		//         item.fillItemCategory(this, p_40778_);
		//      }

		//   }
	
	@Override

	public void fillItemList(NonNullList<ItemStack> items) {
		for(Item item : Registry.ITEM) {
			item.fillItemCategory(this, items);
		}
	    Collections.sort(items, new SortByReg()); 
	}

	
}

 

ok, thanks for you help