Get Task reference to void async method

Question

I have a working .NET5 c# code like below:

class dummy
{
  public async Task CommandAsync(string command, Action<DataTable> action) 
  {...}
}

Above is compiled in a library referenced from another project, and the method is called as below:

var d = dummy();
var commandTask = d.CommandAsync("some command", ProcessResult);
while (!commandTask.Wait(100)) Console.Write(".");

The key point here is that I can get the reference to the Task from a void async function. Above works correctly.

Today when I am trying to write another app, I ran into this error:

Not sure if any difference, but the issue is that now I can't find the way to get the reference to the Task executing the void method RunAsync.