F# equivalent of C# async event handler in Xamarin iOS

Question

This answer shows assigning a button TouchUpInside event handler with the following syntax:

btnSave.TouchUpInside += async (sender, e) => 
{
    await Createuser(); 
};

Is there an equivalent in F#? There does not seem to be a += overload in F#.

I have tried all of the following but the type system always yells at me that the result is not unit

btnSave.TouchUpInside.Add (fun s e -> async { return () })
btnSave.TouchUpInside.Add (fun s e -> async { return () } |> Async.StartAsTask )

The following compiles but throws an expected exception for any actions on the controller because we are no longer on the main UI Thread

btnSave.TouchUpInside.Add (fun s e -> async { return () } |> Async.Start)

I'd like to be able to run async functions with the F# equivalent of async/await without having to constantly marshall back onto the main UI thread similar to the syntac sugar we get in C#