Here’s the new Long-press Back action option.
The Minimize & hide action leaves the app running in the background but removes it from the Recents screen. You can re-open the app via the launcher icon. It requires Android 5.0 or later.
The Start PIP mode action requires Android 7.0+.
I didn’t find any way to trigger split screen on Marshmallow (as far as I’ve seen it requires root anyway).