There are as many "explanations" for the efficacy of psilocybin as there are models of consciousness. The one I like is that the drug causes an increase in neuroplasticity and that allows your brain to reroute its network more easily. I find it does great for helping me decontextualize experiences and strip them of the heavy negative emotional baggage some experiences have.

I don't know, I've heard it works well alongside therapy and having sessions to help integrate the experience. I usually just microdose and meditate with an intention a few timesin the week before a legit trip and let the drugs do their thing. Sometimes it's unpleasant in the moment but I always start a timer when I dose so I have seen over the years that the unpleasant parts are only like 15 minutes to an hour of the 6ish hour experience. Those 15 minutes can feel like forever because it messes with one's perception of time but even that gets less weird with practice.

They are powerful little guys though. I went to church after my most recent trip because it felt really right. That was odd since I'm not a practicing Christian anymore although I don't hate religion by any means I've just never gotten a lot out of it.