https://www.techradar.com/news/android-p-will-indeed-have-a-clear-all-button

We open up too many apps on Android like we open up too many tabs on Chrome, and there was a handy solution: the 'Clear All' button that closes all of open apps.

This button is sorely missing from the Android P beta, which introduces a new interface to the home and recent buttons. It gives you can an overview of all open apps when you swipe up from the bottom of the screen.