Result:

M1M2
M2
M1

Reason:
In the SomeEnd1 method, the M1 task is awaited before the M2 task has been called.

Suggestion:
In the SomeEnd2 method, both tasks are started before awaiting any to complete. Ideally you wouldn’t await each task individually, instead use await Task.WhenAll()… SomeEnd2 would be better like this:

 public async Task SomeEnd2()
 {
 var tasks = new List<Task>();
        tasks.Add(M1());
        tasks.Add(M2());
        await Task.WhenAll(tasks);
 }

The result will be the same, but this pattern will allow you to add tasks as needed without the need to await each individually.

Futher thoughts:
If you needed the result of one asynchronous method before starting another method, you can kick off all non-dependent tasks and then await the task(s) need for the dependent task(s) and still await Task.WhenAll(tasks) before you need the results.

Try the code below, I have added more output lines with some formatting that may help illustrate things a bit.

CAsync2 myc = new CAsync2();
await myc.SomeEnd1();
Console.WriteLine();
Console.WriteLine();
await myc.SomeEnd2();
Console.WriteLine();
Console.WriteLine();
await myc.SomeEnd3();
public class CAsync2
{
 public async Task<string> M1()
 {
 Console.WriteLine("    M1 start");
 var value = Path.GetRandomFileName();
        await Task.Delay(4000);
 Console.WriteLine("    M1 complete");
 return value;
 }
 public async Task M2()
 {
 Console.WriteLine("    M2 start");
        await Task.Delay(200);
 Console.WriteLine("    M2 complete");
 }
 public Task M3(string value)
 {
 Console.WriteLine("    M3 start");
 Console.WriteLine($"    M3 - value = \"{value}\"");
 Console.WriteLine("    M3 complete");
 return Task.CompletedTask;
 }
 public async Task SomeEnd1()
 {
 Console.WriteLine("SomeEnd1 start");
        await M1();
        await M2();
 Console.WriteLine("SomeEnd1 complete");
 }
 public async Task SomeEnd2()
 {
 Console.WriteLine("SomeEnd2 start");
 var tasks = new List<Task>();
        tasks.Add(M1());
        tasks.Add(M2());
        await Task.WhenAll(tasks);
 Console.WriteLine("SomeEnd2 complete");
 }
 public async Task SomeEnd3()
 {
 Console.WriteLine("SomeEnd3 start");
 var tasks = new List<Task>();
 var m1 = M1();
        tasks.Add(m1);
        tasks.Add(M2());
 var m1Result = await m1;
        tasks.Add(M3(m1Result));
        await Task.WhenAll(tasks);
 Console.WriteLine("SomeEnd3 complete");
 }
}

In fact, you don’t need to add the m1 Task to the task list since we are waiting for it to be completed before startng M3.