A recent video made by XDA based on a leaked version of Android Q from January 2019 does not have a 'back' option in its UI navigation functions. The user must now swipe to the left using the 'pill' to return to a second-most recent app. This Q build also has smoother animations for app-switching.
https://www.notebookcheck.net/Android-Q-could-make-the-back-button-obsolete.410361.0.html