Screen pinning, despite the fact that it exists since 2014, is quite unknown. It's a helpful security tool that limits access to your device to just one app – perfect for when someone asks if you want to borrow your phone. While previous versions have kept this function unchanged, the new Android 9.0 Pie multitasking interface is changing the way it works.
Android Pie introduced the Gestennavigation. With this change, Google has made adjustments to the UI, including a major overhaul of the Recent Apps screen. As a result, Google knew that features that included the Recent Apps screen needed to be redesigned, including screen capture. So, for those of you who even know about the feature, here's how screen fix works in Android 9.0.
To enable screen fix on Android Pie, first go to the main settings menu and select "Security & Location". Scroll down and tap "Advanced" to see more options. The last option (which is one reason why many people miss it) is "screen pinning". Select this option and select the check box to enable the feature.