Problem: The Alt keyboard shortcut to manipulate ROIs does not work. This is because the GUI uses the same shortcut for an alternative function (for example move a window around the desktop.
Solution: In KDE you can change the behaviour of the Modifier Key (to alternatively listen to the Meta key). Setting System Settings>Window Behaviour>Modifier key to “Meta” (default is “Alt”) resolves this problem. Note that now the Meta-key (also called Win-key in some keyboards) executes the command of KDE.
If there is a similar setting in Gnome, please add it here.