The only thing I have found is relatively temporary. Follow the other instructions about long pressing the grey bar and you can hide from lock screen. But to get out of notification bar during normal running time, click on the blue question mark next to "system ui" and hit force stop.
This will turn it off but it will come back after you restart your phone/turn it off then back on. I'm not sure yet whether it will come back after your phone sleeps/dozes.
Oh and if you turn off power saving and then turn it back on, this pops up again.
If you are like me a barely ever turn your phone off, and keep power saver turned on all the time, then it works well. Until I find a permanent solution this is it!