Apps and defaults

You can set a browser other than Safari as the app that opens links from Messages, Mail and everywhere else.

Settings > Apps > Default Apps > Browser

Each app has its own switch deciding whether it may use cellular data, so you can restrict a heavy app to Wi-Fi only.

Settings > Cellular > App name

When storage runs low, apps you have not opened in a while are removed but their icons and data stay, so tapping the icon reinstalls them.

Settings > App Store > Offload Unused Apps

Each app's location access is set individually to Never, Ask Next Time, While Using the App, or Always.

Settings > Privacy & Security > Location Services > App name

This switch decides whether apps update themselves in the background or wait for you to update them in the App Store.

Settings > App Store > App Updates

You can set a mail app other than Apple Mail to handle email links and share sheet actions.

Settings > Apps > Default Apps > Mail

Apps, books and music bought on one device can download automatically to your other devices, and a separate switch controls whether that happens over cellular.

Settings > App Store > Automatic Downloads

AutoFill can draw from the built in Passwords app or from a third party password manager you choose.

Settings > General > AutoFill & Passwords