Here's a good article on duel extract vs just a simple decoction.
https://www.realmushrooms.com/is-dual-extraction-necessary-for-mushrooms/
As you do your research I'm sure you will find that there is some debate on whether on not a duel extract is necessary for every type of mushroom. Some mushrooms such as; "cordyceps, lions mane, turkey tail, shiitake and maitake" only contain water soluble compounds (which are extracted with a decoction) while other mushrooms like chaga ALSO contain non water soluble compounds (which have to be extracted with alcohol).
Cheer and best of luck to you on your fungi journey! 😁