@Ron-Z I have had this happen to me a few times with similar road closures in Wales. I generally will make sure that my shaping points will take me to the road (which I think they do from your picture). With the last point before the route, I will make pink with a warning icon and put a note in the waypoint about when the road is expected to open. Additionally at a point just before the detour for the closure, I will also put another point with a warning icon and call it 'Check Road Open' or something similar and I will then receive a verbal warning (settings dependent). The main point is that if you are navigating as a route then the navigation will take you on the route if the road is open when you start the route on your device and the route calculation is performed. Sometimes the roads are not always notified as being formally open but the check point allows me to see what signage is out if the route is open or not.
If you are navigating as route to track then same calculation should happen to generate the track correctly if the road is open. Happy to be corrected if not the case as I am still 'playing' with this new feature. The additional points I suggested will still be useful to check as with a route.
Remember that the web planning tool is just a planner based on published information (visible when selecting traffic) but your device will calculate your route or track on known information at that time when you start the app to navigate. Hope this makes sense and helpful.