yeah, I obviously did it, but afterwards nothing happens... I suppouse that no app is currently making use of it! so it is unuseful at the moment!
the only similar thing I have seen is in game mode. when a notification is received, it's showed similar to floating notifications, but if you click on it, the app is opened in floating mode. I would like to have it always like this, with the bubbles (like Samsung devices with Android Pie).