action_delegate.cs

using System;
class Account
{
    public void Main()
    {
        Action<string> action = (str) => Console.WriteLine(str);
        action("test");
    }
}

​action_delegate.decompiled.cs

using System;
using System.Diagnostics;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Security;
using System.Security.Permissions;

[assembly: CompilationRelaxations(8)]
[assembly: RuntimeCompatibility(WrapNonExceptionThrows = true)]
[assembly: Debuggable(DebuggableAttribute.DebuggingModes.Default | DebuggableAttribute.DebuggingModes.DisableOptimizations | DebuggableAttribute.DebuggingModes.IgnoreSymbolStoreSequencePoints | DebuggableAttribute.DebuggingModes.EnableEditAndContinue)]
[assembly: SecurityPermission(SecurityAction.RequestMinimum, SkipVerification = true)]
[assembly: AssemblyVersion("0.0.0.0")]
[module: UnverifiableCode]
internal class Account
{
    [Serializable]
    [CompilerGenerated]
    private sealed class <>c
    {
        public static readonly <>c <>9 = new <>c();

        public static Action<string> <>9__0_0;

        internal void <Main>b__0_0(string str)
        {
            Console.WriteLine(str);
        }
    }

    public void Main()
    {
        Action<string> action = <>c.<>9__0_0 ?? (<>c.<>9__0_0 = new Action<string>(<>c.<>9.<Main>b__0_0));
        action("test");
    }
}

​​.sharplab.json

{
    "version": 1,
    "target": "C#",
    "mode": "Debug"
}