Some of the recommendations in the list date back to .NET Framework.
Most of the time, it is not something one needs to worry about because actually problematic cases are highlighted by default Roslyn analyzers and will give you a warning on build as well.
Async/await is a superior model that is more flexible and solves more tasks (heh) at hand than green threads which have more limited scope of application, higher base overhead and cannot reach parity at efficiency due to stack state having to be always preserved.