I notice that Valhalla and Graphhopper seem to treat bicycle roads as fine to route through for cars, see e.g. here: Linienstraße. OSRM, though, will route correctly.
In the example, it seems that Valhalla and Graphhopper both ignore at least three tags when routing for cars: bicycle=designated, bicycle_road=yes and vehicle=destination.
report that vehicle=destination is ignored for car routing on their issue tracker? Iff it is not yet reported and this tag is ignored. Note that vehicle=destination blocks only transit traffic.
You can also contribute code fixing the issue.
bicycle=designated does not mean that cars cannot go there, in the same as bicycle=designated on highway=path does not mean that pedestrian traffic is blocked.