I have dug around in Plasma’s effects and among others enabled the effect that allows you to draw on the desktop while holding Super+Shift.
If you additionally press Ctrl it seems to not draw until you move your mouse and press Super+Ctrl+Shift again, then it draws a straight arrow from the first point to the second one.
My suggestion is to make a preview of the arrow that moves around to show how it would appear if you pressed the latter keycombo in just that moment.