Semi.Avalonia/demo/Semi.Avalonia.Demo/ViewModels/ApplicationViewModel.cs

using Avalonia;
using Avalonia.Controls.ApplicationLifetimes;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;

namespace Semi.Avalonia.Demo.ViewModels;

public partial class ApplicationViewModel : ObservableObject
{
    [RelayCommand]
    private void Exit()
    {
        if (Application.Current?.ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
        {
            desktop.Shutdown();
        }
    }
}