It is difficult for me to understand your answer. However, I tried double-clicking the title bar and (finally) noticed the two (or more) window titles under the title bar of the window. Whew! Took me long enough, but thanks to your reply I did notice it.
That alone helps me.
However, double-clicking the title bar simply changes the size of the window, not its contents nor appearance. And I checked out the Dock prefs in System Prefs. That is useful to know about.
So thanks for that.
My wish is not fulfillled, however: two windows side by side, allowing click and drag to move a file from one window to the other.