If you have an application and you want to move it to another screen, you right click on application name bar (the one with minimize,maximize,close buttons) and you select "move to screen". The menu "move to screen" is not available if you right click on application entry on Plasma panel
KDE Frameworks 5.58.0 Qt 5.12.1 Fedora 30
*** This bug has been marked as a duplicate of bug 407647 ***
*** This bug has been marked as a duplicate of bug 383192 ***