Hi @cicisaja! Like I said in the post, it is very important to be sure of what you are eating in the wild. My top advice would be to always consult more than just one source (I have many books and websites that I regularly study). In regards to the birch polypore, it is pretty easy to identify. Not much else looks like it. Always make sure that it is growing on a birch tree. Underneath this fungus, you will see a pure white pore-like underside. The flesh will also be pure white. The cap will vary from light brown to a dark brown as it matures. The picture in the article is of a very young specimen which has not yet acquired the brown coloration on the cap. If you're still not confident, try checking out this article: https://www.wildfooduk.com/mushroom-guide/birch-polypore/
It has loads of great information including a video which will help you identify this fungus properly.

Enjoy!