Why HasErrors not change true when return an error ValidationResult?

[kyuranger]

Here is my code:

public class TestVM:ObservableValidator
{
string _IP = "";        
[CustomValidation(typeof(TestVM), nameof(ValidateIP))]
public string IP {
    get => _IP;
    set {                
        if (_IP != value)
        {
            _IP = value;
            OnPropertyChanged();                    
            OnPropertyChanged("HasErrors");
        }
    }
}

public static ValidationResult ValidateIP(string Name, ValidationContext Context)
{            
    string Pattern = @"^((25[0-5]|2[0-4]\d|[01]?\d\d?)\.){3}(25[0-5]|2[0-4]\d|[01]?\d\d?)$";
    if (Regex.IsMatch(Name, Pattern)&&!string.IsNullOrEmpty(Name))
    {                                
        return ValidationResult.Success;
    }            
    return new("IP Error");
}
}

The version of Community Toolkit.MVVM I am using is 8.2.2. And I test my code in Avalonia(a .Net crossplatform framework).
Here is my XAML:

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
		xmlns:Local="using:AvaloniaApplication1"
        x:Class="AvaloniaApplication1.MainWindow"
		x:DataType="Local:ViewModel"
        Title="AvaloniaApplication1">

	<Grid RowDefinitions="auto,auto">
		<TextBox Text="{Binding IP,Mode=TwoWay}"></TextBox>
		<TextBlock Grid.Row="1" Text="{Binding HasErrors,StringFormat='HasErrors:{0}'}"></TextBlock>
	</Grid>
</Window>

And here is code-behind:
using Avalonia.Controls;
using Avalonia.Media;
using Avalonia.Threading;
using CommunityToolkit.Mvvm.ComponentModel;
using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;
using static AvaloniaApplication1.ViewModel;

namespace AvaloniaApplication1
{
    public partial class MainWindow : Window
    {        
        public MainWindow()
        {
            InitializeComponent();            
            this.DataContext= new TestVM();           
        }
        
    }    
}

As you see, no matter whether the value validates success or not, the HasErrors are always false.

There are some properties on a page. What I want to do is keep the IsEnabled of the Apply button to false when there is a validate error of the property.

What's wrong with my code?