Ubuntu MATE 18.04, using Mutiny layout. I would like to add a workspace switcher to the left-hand Launcher panel. This has been problematic. I'm not sure whether these are actually separate issues, nor am I sure which packages they should actually be filed against.
Issue 1: this is almost impossible. To add a new panel applet, one right-clicks on the panel and chooses "Add to panel". However, this only works if one is clicking on the panel itself, not an applet _within_ that panel. And the left-hand Launcher panel doesn't have any spare space; all space within it is taken up by Brisk menu, the Wastebasket applet, and (mostly) the Dock applet. So there's nowhere to click to add to this panel. I eventually discovered that the very bottom left corner is not owned by the Wastebasket applet (which arguably it should be!) so one can add to this panel by right-clicking there, but there should be a much easier way to do this.
Issue 2: once a workspace switcher is added to the panel as above, the Wastebasket applet disappears. I do not know whether this is because it's actually gone, or if it's pushed off the bottom of the screen (the left-hand panel is not scrollable as far as I can tell, and does not collapse when oversized as per the Unity Launcher that it's imitating, so there's no way to get at applets that are off the bottom of the screen).
Perhaps right-clicks on an "empty" area of a widget should add the panel's "add to panel" entry to that menu? Since the menu includes "lock to panel" and the like, it's being provided _by_ the panel, not wholly by the widget itself.