Hello,
Found it, please have a look here:
How to get to Android back button on Surface Duo? - Microsoft Community
Tip #1: Turn off navigation gestures
By default, Surface Duo uses swipe gestures for navigation. Besides having a learning curve, some people don't like swiping to go back or bring up the app switcher. But you don't have to use that nav gestures at all and can instead rely on virtual buttons for back, home, and app switcher. Here's how:
- Go to Settings > System > Gestures > System navigation
- Enable 3-button navigation
That's it. Some of you may prefer this navigation method, while others may appreciate how (at least to me) it feels smoother when jumping around between apps. The only real downside is you lose a few pixels of vertical space due to the navbar. Either way, it's good to know your options.
Thanks.