I like how it boils down to "you just have to know." And those who know don't like to share because they like to know that they know and you don't know.
Mentioned above, but got into foraging lightly a couple years ago and found the community to be absolutely welcoming and open. I have not gotten a hint of not wanting to share.
That is usually quite far from the truth. But there are many factors beyond looks that you need to consider, e.g. smell, location, how it reacts when you scratch it, whether some bits are sticky or not, etc. No app will ever work simply because a picture is not enough.
Nobody can tell you all of it like that, not because they don’t want to, but simply because this is just an enormous amount of information that is very context sensitive. There are some very good books if you want to learn. Otherwise, join a bunch of people when they go out looking for mushrooms, the best way to learn is by following them. There really is no substitute.
