@BMWBiker58 Provided your route doesn’t wind its way around the closed motorway exit like a snail, I don’t see any danger here.
As already described, the app will guide you to the selected waypoint, and it doesn’t matter whether that’s a shaping or a Via point.
In your example, you couldn’t leave the motorway at the closed exit... as soon as you selected the next exit and left the motorway, you’ll be guided to the new selected point, possibly just outside the motorway, passing close to your closed exit, but of course only if your destination is near the closed exit.
If your destination is not next to the closed exit, you will not be guided there.
To be absolutely sure that you are not guided back, please skip one or two more waypoints than might be necessary.
The app will definitely not navigate you to the closed exit...
It is understandable that you would want to inform the app that this exit is closed, but it is absolutely not necessary.