Currently, as of v0.26.5, we're setting aria-haspopup on PopupButtonWidget, introduced in T87694
Not only do we set it on a non-focusable element (the surrounding span). We also don't change indicate the child link as triggering element clearly. Setting aria-haspopup there is of no use for screenreaders.
Apart from mid-future accessibility and usability improvements in T185752, it would be better to add an id to the description-holding div and add an aria-describedby=ID to the link on hover and focus.