Android and iOS systems have their own security policies involving user information or device hardware. The purpose of permission is to protect the privacy of a user. An app, whether native or not, must request permission to access user data, such as the camera, for example.
In iOS's recent versions, you must include the usage description in the ios/Runner/Info.plist file keys for the types of data the app needs to access, or it will crash. To access the camera, for example, it must include NSCameraUsageDescription.
You can check out the available permissions for iOS here: https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CocoaKeys.html#//apple_ref/doc/uid/TP40009251-SW1.
In Android, the android/app/src/main/AndroidManifest.xml file is where permissions are listed. Android has the concept of...
