I found a simple solution: Put youtube in multitask (half screen), press the horizontal line that divides the two apps, and you will see an icon with one square inside another, this button will make a floating window of youtube (or the last app you touch)
It's faster to go to multi task menu, hold a finger on an app and drag it to the square in the middle for pop out view.
BTW, did you guys noticed three-dot menu in multi task menu? You can change card view to list view which is way more conivninet IMO.