参考

こちらの記事を参考にさせていただきました

目的

usingの後にawaitを呼んだ場合に、対応するDisposeはどのスレッドで呼ばれるのか確認しました

結果

ConfigureAwait(false)をつけないでawaitした場合、usingを呼んだスレッドに戻ってからDisposeが呼ばれた
ConfigureAwait(false)をつけてawaitした場合、usingを呼んだスレッドに戻らずにDisposeが呼ばれた
using宣言と、スコープを指定するusing、usingと同等のtry&finallyの置き換えで同様の動作となった

確認用コード

MainWindow.xaml.cs

using System.Diagnostics;
using System.Windows;

namespace WpfApp2
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public static class DebugLogger
        {
            public static void LogDebug(string message)
            {
                int threadId = Thread.CurrentThread.ManagedThreadId;
                Debug.WriteLine($"[Thread {threadId}] {message}");
            }
        }

        public class MyData : IDisposable
        {
            public string Data { get; set; } = "Initial Data";

            public MyData()
            {
                DebugLogger.LogDebug("MyData Constructor Called");
            }

            public void Dispose()
            {
                DebugLogger.LogDebug("MyData Disposed");
            }
        }

        public MainWindow()
        {
            InitializeComponent();
        }

        public async Task ProcessDataAsync(MyData data)
        {
            await Task.Run(() =>
            {
                DebugLogger.LogDebug("Processing data...");
                Thread.Sleep(1000);
                data.Data = "Processed Data";
                DebugLogger.LogDebug($"Data updated to: {data.Data}");
            });
        }

        private async void Button1_Click(object sender, RoutedEventArgs e)
        {
            DebugLogger.LogDebug("//-----------------------");
            DebugLogger.LogDebug("Button1_Click Starting...");
            using var myData = new MyData();
            await ProcessDataAsync(myData);
            DebugLogger.LogDebug("Button1_Click Finished.");
        }

        private async void Button2_Click(object sender, RoutedEventArgs e)
        {
            DebugLogger.LogDebug("//-----------------------");
            DebugLogger.LogDebug("Button2_Click Starting...");
            using var myData = new MyData();
            DebugLogger.LogDebug("ProcessDataAsync Starting...");
            await ProcessDataAsync(myData).ConfigureAwait(false);
            DebugLogger.LogDebug("Button2_Click Finished.");
        }

        private async void Button3_Click(object sender, RoutedEventArgs e)
        {
            DebugLogger.LogDebug("//-----------------------");
            DebugLogger.LogDebug("Button3_Click Starting...");
            using (var myData = new MyData())
            {
                await ProcessDataAsync(myData);
            }
            DebugLogger.LogDebug("Button3_Click Finished.");
        }

        private async void Button4_Click(object sender, RoutedEventArgs e)
        {
            DebugLogger.LogDebug("//-----------------------");
            DebugLogger.LogDebug("Button4_Click Starting...");
            using (var myData = new MyData())
            {
                await ProcessDataAsync(myData).ConfigureAwait(false);
            }
            DebugLogger.LogDebug("Button4_Click Finished.");
        }

        private async void Button5_Click(object sender, RoutedEventArgs e)
        {
            DebugLogger.LogDebug("//-----------------------");
            DebugLogger.LogDebug("Button5_Click Starting...");
            MyData? myData = null;
            try
            {
                myData = new MyData();
                DebugLogger.LogDebug("ProcessDataAsync Starting...");
                await ProcessDataAsync(myData);
                DebugLogger.LogDebug("ProcessDataAsync Finished.");

            }
            catch (Exception ex)
            {
                DebugLogger.LogDebug($"An error occurred: {ex.Message}");
            }
            finally
            {
                if (myData != null)
                {
                    myData.Dispose();
                    DebugLogger.LogDebug("MyData disposed in finally block.");
                }
                DebugLogger.LogDebug("Button5_Click Finished.");
            }
        }

        private async void Button6_Click(object sender, RoutedEventArgs e)
        {
            DebugLogger.LogDebug("//-----------------------");
            DebugLogger.LogDebug("Button6_Click Starting...");
            MyData? myData = null;
            try
            {
                myData = new MyData();
                DebugLogger.LogDebug("ProcessDataAsync Starting...");
                await ProcessDataAsync(myData).ConfigureAwait(false);
                DebugLogger.LogDebug("ProcessDataAsync Finished.");
            }
            catch (Exception ex)
            {
                DebugLogger.LogDebug($"An error occurred: {ex.Message}");
            }
            finally
            {
                if (myData != null)
                {
                    myData.Dispose();
                    DebugLogger.LogDebug("MyData disposed in finally block.");
                }
                DebugLogger.LogDebug("Button6_Click Finished.");
            }
        }
    }
}

出力結果

[Thread 1] //-----------------------
[Thread 1] Button1_Click Starting...
[Thread 1] MyData Constructor Called
[Thread 15] Processing data...
[Thread 15] Data updated to: Processed Data
[Thread 1] Button1_Click Finished.
[Thread 1] MyData Disposed
[Thread 1] //-----------------------
[Thread 1] Button2_Click Starting...
[Thread 1] MyData Constructor Called
[Thread 1] ProcessDataAsync Starting...
[Thread 3] Processing data...
[Thread 3] Data updated to: Processed Data
[Thread 3] Button2_Click Finished.
[Thread 3] MyData Disposed
[Thread 1] //-----------------------
[Thread 1] Button3_Click Starting...
[Thread 1] MyData Constructor Called
[Thread 3] Processing data...
[Thread 3] Data updated to: Processed Data
[Thread 1] MyData Disposed
[Thread 1] Button3_Click Finished.
[Thread 1] //-----------------------
[Thread 1] Button4_Click Starting...
[Thread 1] MyData Constructor Called
[Thread 3] Processing data...
[Thread 3] Data updated to: Processed Data
[Thread 3] MyData Disposed
[Thread 3] Button4_Click Finished.
[Thread 1] //-----------------------
[Thread 1] Button5_Click Starting...
[Thread 1] MyData Constructor Called
[Thread 1] ProcessDataAsync Starting...
[Thread 3] Processing data...
[Thread 3] Data updated to: Processed Data
[Thread 1] ProcessDataAsync Finished.
[Thread 1] MyData Disposed
[Thread 1] MyData disposed in finally block.
[Thread 1] Button5_Click Finished.
[Thread 1] //-----------------------
[Thread 1] Button6_Click Starting...
[Thread 1] MyData Constructor Called
[Thread 1] ProcessDataAsync Starting...
[Thread 15] Processing data...
[Thread 15] Data updated to: Processed Data
[Thread 15] ProcessDataAsync Finished.
[Thread 15] MyData Disposed
[Thread 15] MyData disposed in finally block.
[Thread 15] Button6_Click Finished.