cirnogodot/Scripts/UI/StatusMenu.cs

using Godot;
using System;
using Cirno.Scripts.Resources;

public partial class StatusMenu : PanelContainer
{
    [Export] public StringName HealthExpansionName { get; private set; }
    
    [Export] public StringName ShieldExpansionName { get; private set; }

    [Export] public Button HealthExpansionCounter { get; private set; }
    
    [Export] public Button ShieldExpansionCounter { get; private set; }
    
    public override void _Ready()
    {
        CallDeferred(MethodName.InitializeDeferred);
    }

    public override void _ExitTree()
    {
        InventoryManager.Instance.ItemAdded -= InstanceOnItemAdded;
    }

    private void InitializeDeferred()
    {
        var healthExpansions = InventoryManager.Instance.GetItemCount(HealthExpansionName);
        var shieldExpansions = InventoryManager.Instance.GetItemCount(ShieldExpansionName);

        HealthExpansionCounter.Text = $"x{healthExpansions}";
        ShieldExpansionCounter.Text = $"x{shieldExpansions}";
        
        InventoryManager.Instance.ItemAdded += InstanceOnItemAdded;
    }

    private void InstanceOnItemAdded(LootItem item, int currentamount)
    {
        if (item.ItemKey == HealthExpansionName)
        {
            HealthExpansionCounter.Text = $"x{currentamount}";
        }
        else if (item.ItemKey == ShieldExpansionName)
        {
            ShieldExpansionCounter.Text = $"x{currentamount}";
        }
    }
}