How to stop apps from refreshing in background when background refresh is OFF already iPhone 11

First, there is no such thing as an app that is “closed”. Any app that can receive a notification or update will be launched whether open or closed. You also need to be specific about “doing anything in background”. Any app that receives a notification or update will unsuspend to save it, but this is a very short (milliseconds) process that uses no energy. If your definition of “doing anything in background” includes saving a notification or pushed data then there is no way to prevent that except to not have any apps on your phone that update from push events or notifications.

As far as your “knowledge or permission” is concerned you granted permission when you accepted Apple’s terms by tapping “accept” when setting up your iPhone.

You misunderstand background app refresh, which isn’t surprising, because it really isn’t explained well anywhere. What it controls is non-event-driven updates. That is, an app that decides on its own to do some scheduled processing; very few apps actually use this feature, which wasn’t in the original implementation of iOS. Apps that refresh because they received a notification such as a text, email, periodic weather report, stock update, etc are not controlled by background app refresh settings; they are responding to a stimulus. The only way you can stop apps from even-driven updates is to delete the app. Even closing it in the App Switcher will not stop apps from receiving updates.

For an app like Mail you can set “fetch” to manual; if you do, it will only download email when you open the app. But that isn’t an option for text messages, weather updates and other dynamically updated content because users expect those functions to be accurate when they are opened.

For other apps you can go to Settings/Notifications and turn off all notifications for the app; this will prevent them from responding to new information.

Lawrence Finch wrote:

You misunderstand background app refresh, which isn’t surprising, because it really isn’t explained well anywhere. What it controls is non-event-driven updates. That is, an app that decides on its own to do some scheduled processing; very few apps actually use this feature, which wasn’t in the original implementation of iOS. Apps that refresh because they received a notification such as a text, email, periodic weather report, stock update, etc are not controlled by background app refresh settings; they are responding to a stimulus. The only way you can stop apps from even-driven updates is to delete the app. Even closing it in the App Switcher will not stop apps from receiving updates.

That's an extremely enlightening explanation.

You are assuming that there is a reason not to allow apps to update periodically and to not process notifications. However, there is no meaningful reason to block updates; it is one of the things that makes smartphones as versatile as they are. And, technically, it is NOT doing something in background; it is sharing processor cycles with other functions. iOS itself runs CONTINUOUSLY in background; if it stopped the phone wouldn’t work at all. Many apps can’t do their job if they don’t run in background; the phone and text apps, for example wouldn’t work if they didn’t have processes running in background. No communication apps could work if they didn’t run in background, including WhatsApp, Facebook Messenger, Telegram, Signal, Skype... The communications subsystems always run in background; Wi-Fi, Bluetooth, BonJour, cellular voice, cellular data, mail, FaceTime. Find My wouldn’t work if it didn’t run in background.