An async method cannot return any type that has an accessible GetAwaiter method

It says here:

Async methods can have the following return types:

• Task, for an async method that performs an operation but returns no value.

• Task <TResult>, for an async method that returns a value.

• void, for an event handler.

• Starting with C# 7.0, any type that has an accessible GetAwaiter method. The object returned by the GetAwaiter method must implement the System.Runtime.CompilerServices.ICriticalNotifyCompletion interface.

• Starting with C# 8.0, IAsyncEnumerable<T>, for an async method that returns an async stream.

Question. How to understand the phrase: "Asynchronous methods can have the following return types: ... any type that has an accessible GetAwaiter method", if the actual is not?

This code is not working:

using System.Runtime.CompilerServices;

async A Method() //Error CS1983 The return type of an async method must be void, Task, Task<T>, a task-like type, IAsyncEnumerable<T>, or IAsyncEnumerator<T>
{
    await new A();
}

class A
{
    public TaskAwaiter GetAwaiter()
    {
        return new TaskAwaiter();
    }
}