Hi, I want to set up the following shortcut: the mouse middle button (which is one of my pen's button), will act as the undo tool (control z). But I cannot do it, when I press the pen's button, nothing is registered in the shortcut editor. In the "configure krita" I cannot see the undo option, only some options related to the current selected brush

Sorry, that this is not exactly your question answer, but maybe useful.

I have mapped undo to 'Z' instead Ctrl+Z (I have non-drawing hand on keyboard anyway, need a lot of shortcuts), and this reduces number of key-presses by factor of two