You will eventually notice that each time you swipe up to open multitasking view, the app icons just below your open apps are always changing. That's because Android Pie 9.0 is constantly learning and suggesting apps it thinks you will want to open based on your usage habits and the time of day.

In the App Drawer you will see similar shortcuts, some of which go further than opening an app. For example, if you send a lot of messages to a contact in Facebook, a shortcut to that message thread will show up.