Into the Gender-Swap Forest: Book 1 by Sylvia Wetwood

The Woods of Desire. The internet claims that it can unleash the innermost yearning of one's heart. But you don't often find the truth on the internet. Darien just enjoys a good hike, especially alongside his best friend, William. They enter the mysterious woods, and soon, Darien is changing into a woman. Darien's innermost desires are going to come out, and his body is going to become totally new—gorgeous, female, and craving some attention.