Navigationsgester is now a thing on Android Pie. See the pill-shaped button at the bottom of the screen? It replaces the three buttons previously used on Android.
The function is optional and off by default. You can enable it by going to Settings > Gesturer > Turn up on the home screen and switch the switch.
Of course, different phone manufacturers will have different interpretations of how gestures will work on Android Pie.
For example, Google's Pixel 3 and Pixel 3 XL are all-in on gestures and have no option to turn them off. Samsung, on the other hand, has a unique setting for gestures in its One UI beta.