⭐ The app is tested on Android 9 Pie on Note 8 it is working without any major problem.

⚠️ When you enable fullscreen mode on some devices you can see a black area below some apps instead of the navigation bar. This is because some apps do not support fullscreen aspect ratio. In this situation you can look for a menu about fullscreen apps in settings of your device if it supports. For example in note8 you can force apps to be shown in fullscreen aspect ratio following "Settings > Display > Fullscreen apps". Also on some devices (for instance on note 8) navigation and status bars ar forced to be shown only on home screen this is not an unexpected behaviour...

⚠️ Some device models (not related to android versions) are NOT RESPONDING to mode change requests made by the app. So the app MAY NOT WORK on some device models.

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You can hide status bar and navigation bar (if exists) on your device for fullscreen experience in all apps. When you need the bars in full screen mode you can swipe from top or bottom edges of the screen to show them temporarily.

You can also prevent possible screen burns 🔥 enabling fullscreen mode. Static views like status or navigation bars can cause permanent damages on your screen. This defect is known as "screen burn" or "ghost screen"👻. You can use this app to hide these bars.

⚠️ Please note that before installing the app; it requires a permission that can be given only using ADB (ADB is NOT root) from a PC and also usb debugging mode to be enabled. These are simple steps that will take no more than 2-3 minutes. Instructions are given in the app.
Enabling usb debugging mode on your phone:
https://developer.android.com/studio/debug/dev-options#enable
Minimal ADB Tool:
https://forum.xda-developers.com/showthread.php?t=2317790

There are many apps that offer fullscreen modes on the market. But turning fullscreen mode on may break screen layout on some devices (for example on Samsung Note 8 or S8) when the keyboard is shown in some apps. Also the keyboard sometimes covers text that is being written in fullscreen mode.

You can enable fullscreen mode along with the keyboard support feature which prevents layout breaks when the keyboard is shown. With this feature enabled the app disables fullscreen mode when the keyboard is shown and re-enables when it is hidden.

The app is free but the keyboard support is paid (a symbolic price to support the developer). You can enable the "Keyboard support" feature for 30 seconds periods to determine if the app is working as you expected on your device before buying that feature. This feature may not work on some device models...