The short answer is that some elements cannot be used to trigger workflows, such as the Link element. I think the SlideBarMenu icon is hard-wired to the open/close action of the bar, so that may be why you can’t use it to trigger a workflow. Just speculating.
I would say the workaround is probably to not use the SlideBarMenu, but build it yourself out of Bubble elements. Not ideal, but not sure how else to go about it.