On MicrosoftEdge/MSEdgeExplainers#441, @carmacleod mentioned:

I didn't see any mention in the explainer of where focus goes after the popup is hidden (i.e. in the case where focus was moved into the popup and didn't just stay on the anchor).

Maybe it's just left up to the author, but if the author doesn't manage focus on hide (which happens), then I think there's an opportunity for a nice default behavior, which is to return focus to the anchor, if there is one. It would be good if the "focus after hide" behavior was explicit in the explainer (perhaps in the Dismissing the popup section).

This seems like a good behavior from a usability/accessibility perspective, assuming that the popup didn't dismiss because the user moved focus out of the popup explicitly.