Google Assistant is getting a new feature on Pixel 4

Starting today, Pixel 4 users can add another new feature to the list of exclusive improvements they benefit from: support for three-button navigation. The latest Google app, which isn't even the most stable, is adding three-button navigation support for Google Assistant, which can be triggered using the hotword (Ok Google) or hold your finger on the home button.
With 3-button navigation, you can switch apps with buttons at the bottom of the screen, go Back or Home. It's a different way to control Google Assistant that doesn't involve gestures, but if you don't like, you can always return to gesture navigation.