Benny, this must be edited in OpenStreetMaps, to indicate private road. Are you familiar with OSM? If you don’t want to try it yourself, I can make an edit for you. This way they will disappear from CityStrides after the next load of Sigtuna. I see it was last update May 12, it nomally takes 5-6 weeks to the next load
I have updated this part of the road to Private in OSM for you. It’s good to be able to make smaller edits in OSM as a strider, you can check this article