In Catalina, regulating the width of the window space is a bit different.
The feature is called Snap! A white frame points to the current selection.
At this point, I have no idea how to explain to get the right trouble shooting support.
Two windows can be displayed split screen, or four can be displayed in a quadrant set up.
Dragging it to the top of the screen will make the window fill the entire screen.
As the cursor reaches the corner, the screen will flash and you'll see an outline of where the window will appear.
How to fit two windows on one screen on a Mac? Select the one you want to add to the other side of the screen.
When doing a presentation and connecting your computer to a projector, duplicate displays are useful for showing others what you are viewing on your computer screen.