Ask HN: Diff Between Android vs. iOS App Permissions

I am trying to understand how strong or restrictive are the OS’s with regards to what the apps can do.

The question stems from the fact how important the phones are wrt to personal data. If there are two apps App 1 and App 2. What all can app1 access from app2 on Android vs iOS? What data can all apps access?

At its core I am trying to understand by installing different apps on my phone what all am I really saying yes to sharing with that app. Is it limited to common things like contacts and generic files folder or is it also that plus the data stored in other apps (say journal apps, text notes etc)

If there are articles / short books that explain this please let me know of it.