C# Online Compiler | .NET Fiddle

using System;
using System.Runtime.CompilerServices;
using System.Text;
					
public class Program
{
	public static void Main()
	{
		var logger = new Logger();
		logger.LogMessage(LogLevel.Critical, "Critical messsage");
		Console.WriteLine("");
		logger.LogMessage(LogLevel.Critical, $"Critical messsage {DateTime.Now}");
		Console.WriteLine("");
		logger.LogMessage(LogLevel.Information, $"Information messsage {DateTime.Now}");
	}
}

public enum LogLevel
{
    Off,
    Critical,
    Error,
    Warning,
    Information,
    Trace
}

public class Logger
{
    public LogLevel EnabledLevel { get; init; } = LogLevel.Error;

    public void LogMessage(LogLevel level, string msg)
    {
		Console.WriteLine("LogMessage string version");
        if (EnabledLevel < level) return;
        Console.WriteLine(msg);
    }
	
	public void LogMessage(LogLevel level, [InterpolatedStringHandlerArgument("", "level")]LogInterpolatedStringHandler builder)
    {
		Console.WriteLine("LogMessage interpolated string version");
        if (EnabledLevel < level) return;
        Console.WriteLine(builder.GetFormattedText());
    }
}

[InterpolatedStringHandler]
public struct LogInterpolatedStringHandler
{
	StringBuilder builder;
	private readonly bool enabled;
	public LogInterpolatedStringHandler(int literalLength, int formattedCount, Logger logger, LogLevel logLevel) 
	{
		enabled = logger.EnabledLevel >= logLevel;
		builder = new StringBuilder(literalLength);			
	}
	
	public void AppendLiteral(string s) 
	{
		if(!enabled) return;
		Console.WriteLine($"Append Literal {s}");
		builder.Append(s);
	}
	
	public void AppendFormatted<T>(T t)
	{
		if(!enabled) return;
		Console.WriteLine($"Append Formatted {t}");
		builder.Append(t.ToString());
	}
	
	internal string GetFormattedText() => builder.ToString();
}

 
using System;
using System.Runtime.CompilerServices;
using System.Text;
                    
public class Program
{
    public static void Main()
    {
        var logger = new Logger();
        logger.LogMessage(LogLevel.Critical, "Critical messsage");
        Console.WriteLine("");
        logger.LogMessage(LogLevel.Critical, $"Critical messsage {DateTime.Now}");
        Console.WriteLine("");
        logger.LogMessage(LogLevel.Information, $"Information messsage {DateTime.Now}");
    }
}
​
public enum LogLevel
{
    Off,
    Critical,
    Error,
    Warning,
    Information,

Cached Result

Environment version: .NET 9.0.0 (9.0.0)
Newtonsoft.Json version: Newtonsoft.Json, Version=12.0.0.0, Culture=neutral, PublicKeyToken=30ad4fe6b2a6aeed

Result of serializing CA:
{"_x":{"isB":true}}
Result of serializing CB:
{"_x":{}}