The Flight Planner currently supports this functionality. When you use the Reverse button in the Route window, the Nav Log is automatically updated to list the waypoints in the reverse order. If the Nav Log does not automatically update for some reason, there is a Refresh button at the top right of the Nav Log window that will force the route to update.
Where is the Reverse Button and what is the route window?
The Reverse button is located in the "Route" window which is part of the sidebar on the left side of the screen. I have indicated the Reverse Route button with the red arrow in the screenshot below.
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