https://wccftech.com/how-to-enable-and-use-gesture-android-pies-gesture-navigation/

Gesture navigation is one of the most prominent changes brought on by Android Pie. However, it’s not enabled by default just yet. So, here’s how to turn on gesture navigation:

To enable Android Pie’s gesture navigation is to you need head over to the settings menu on your device. On a Google Pixel, you can either use the settings icon within the app drawer or press the settings icon in the quick settings menu.