There have been discussions on that in the old forum, maybe i do not have the latest status here.
Having planned a route from A to B, i can insert intermediate waypoints by address or by tapping on the map screen (not by dragging to route on the map though). I can switch the waypoint to a stopover (or vice versa) by tapping it and change its type. I also can delete this intermediate by this.
(1) I can only do these changes while in planning mode, not in navigation with map mode. In special i cannot tap the map (for tapping an existing intermediate to change its properties).
(2) I also cannot do this while in navigation with roadbook (which might the better way for selection of waypoints). On the other hand, i can select calculated route segments listed here for skipping them or marking them as blocked.
It would be a nice feature, to have in (2) the waypoints (or stopovers) being selectable and to change their type or delete them then.