LogError不是一个ILogger方法，所以当你试图检查这个方法是用某些参数调用的时候，NSubstitute会试图以某种方式处理它（我不知 prop 体是怎么做的），但失败了。
LogError扩展方法的代码为：

public static void LogError(this ILogger logger, string message, params object[] args)
{
  if (logger == null)
    throw new ArgumentNullException("logger");
  logger.Log<object>(LogLevel.Error, (EventId) 0, (object) new FormattedLogValues(message, args), (Exception) null, LoggerExtensions._messageFormatter);
}

因此，您必须检查Log方法是否被调用。
我把你的例子简化了一点，我想思路应该很清晰。

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();

        var logger = Substitute.For<ILogger>();
        try
        {
            Create(logger);
        }
        catch
        {
            logger.CheckErrorMessage("My Message");
        }
    }

    public string Create(ILogger logger)
    {
        try
        {
            throw new Exception("My Message");
        }
        catch (Exception e)
        {
            logger?.LogError(e.Message);
            throw new Exception("An error occurred while attempting to create a user.", e);
        }
    }
}

public static class TestExtensions
{
    public static void CheckErrorMessage(this ILogger logger, string message)
    {
        logger.Received().Log(
            LogLevel.Error,
            Arg.Any<EventId>(),
            Arg.Is<object>(o => o.ToString() == message),
            null,
            Arg.Any<Func<object, Exception, string>>());
    }
}

看起来接受的答案在.NET Core 3或.NET 5中不起作用。
以下是在github issue中找到的解决方法
创建新的MockLogger类

public abstract class MockLogger : ILogger
{
    void ILogger.Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter) => 
        Log(logLevel, formatter(state, exception));

    public abstract void Log(LogLevel logLevel, string message);

    public virtual bool IsEnabled(LogLevel logLevel) => true;

    public abstract IDisposable BeginScope<TState>(TState state);
}

用新的模拟记录器替换模拟记录器

// Old 
// var logger = Substitute.For<ILogger>();
// New
var logger = Substitute.For<MockLogger>();

使用新的记录器检查调用

logger.Received().Log(LogLevel.Error, Arg.Is<string>(s => s.Contains("some log message")));

要使用泛型ILogger<T>，只需将类更改为

public abstract class MockLogger<T> : ILogger<T>

这是我的方法，它走得更远。扩展Githhub问题。
第一个记录器：

using Microsoft.Extensions.Logging;

public abstract class MockLogger<T> : ILogger<T>
{
    void ILogger.Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception? exception, Func<TState, Exception?, string> formatter)
    {
        var unboxed = (IReadOnlyList<KeyValuePair<string, object>>)state!;
        string message = formatter(state, exception);

        this.Log();
        this.Log(logLevel, message, exception);
        this.Log(logLevel, unboxed.ToDictionary(k => k.Key, v => v.Value), exception);
    }

    public abstract void Log();

    public abstract void Log(LogLevel logLevel, string message, Exception? exception = null);

    public abstract void Log(LogLevel logLevel, IDictionary<string, object> state, Exception? exception = null);

    public virtual bool IsEnabled(LogLevel logLevel)
    {
        return true;
    }

    public abstract IDisposable BeginScope<TState>(TState state);
}

现在使用：

MockLogger<Service> logger = Substitute.For<MockLogger<Service>>();
logger.IsEnabled(LogLevel.Error).Returns(true);

string originalFormat = "Service returned error with code: '{statusCode}' and reason: '{reason}'";
var statusCode = HttpStatusCode.BadRequest;
string reason = "The reason...";

string message = $"Service returned error with code: '{(int)statusCode}' and reason: '{reason}'";

// Assert
logger.Received(1).Log(
            LogLevel.Error,
            Arg.Is<IDictionary<string, object>>(
                dict =>
                    dict.Any(kv => kv.Key == "{OriginalFormat}" && (string)kv.Value == originalFormat) &&
                    dict.Any(kv => kv.Key == "statusCode" && (int)kv.Value == (int)statusCode) &&
                    dict.Any(kv => kv.Key == "reason" && (string)kv.Value == reason)));

logger.Received(1).Log(LogLevel.Error, message);
logger.Received(1).Log();

它允许单独测试日志参数。

使用下面的名称空间
使用NSubstitute.ExceptionExtensions;
并更新代码以引发异常而不是返回异常。
_mongoContext.InsertOne（newUser）.Throw（exception）;