I personally haven't heard of the win Hoff method, but I am familiar with a few other breathing techniques that have made the rounds for helping with stress and anxiety which ultimately improves the immune system and helps with sleep.
One of them is the box breathing method that seems to be quite effective.
The scientific basis for why breathing techniques can be so effective is that they help activate the parasympathetic nervous system which is the part of the body responsible for calm and relief.
yep, there is a big toolbox available to humans that we seem to rarely use!