When I bought a new display I put the old, smaller one, to the right of the new screen And I set the new screen vertically, like this:
You get there via Windows, Einstellungen, Systemsteuerung, Darstellung und Anpassung, Anzeige, Bildschirmauflösung (see top line), Anzeigeeinstellungen anpassen.
In my use the old screen constantly shows the e-mail input.
Note that you can move screen 2 (in this case) around; to the left or right, and especially up or down. If you place it for the system proportionally where it is in reality, you won’t have to search for your mouse pointer when you want to change from one screen to the other. You can test this directly while adapting the position of screen 2.