WPFタイマーを試す。

dotnet new wpf -n SampleWpfTimer
cd SampleWpfTimer
code .

<Window x:Class="SampleWpfTimer.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        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"
        xmlns:local="clr-namespace:SampleWpfTimer"
        mc:Ignorable="d"
        FontSize="12pt"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <StackPanel>
            <TextBox x:Name="TextBox1" Text="" />
        </StackPanel>
    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

using System.Windows.Threading;

namespace SampleWpfTimer
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            var _timer = new DispatcherTimer();

            int count = 0;
            int count_max = 65535;
            _timer.Interval = new TimeSpan(0, 0, 1);
            _timer.Tick += (s, e) =>
            {
                count = count + 1;
                if (count > count_max) { count = 0; }
                TextBox1.Text = String.Format("{0}", count);
            };
            _timer.Start();

            this.Closing += (s, e) =>
            {
                _timer.Stop();
            };
        }
    }
}