[jm666]

Effects of Wim Hof method are very much backed by rigorous scientific studies, see e.g. this is a good overview of the papers, or read them yourself.

https://scienceofparkinsons.com/2020/02/06/wim-hof/

My conclusion is that some effects are very real, according to best available science. But You have to filter that from Wim Hof's persona & explanation style, which to me often feels very hand-wavy & daresay sometimes even esoteric & his explanations/rationalisations are sometimes clearly off. (e.g. he often says that the breathwork/hyperventilation increases amount of oxygen delivered to cells, while in reality it is the opposite due to Bohr effect). But he imo definitely is onto something with the practice.