6.959 adds a feature I have always wanted but only recently came across a way of making it possible: virtual side screens. I have used it all the time since I created it, especially while on my Macbook without external display it has been amazing.
Using the predefined action "Show / Hide Side Screen" you can slide in a virtual screen in which you can place windows in - it auto arranges them above each other. These windows will stay fully interactive, just tucked away in that little slide-in panel. Have a look at this video:
This might require a current macOS version to work