bicycle=unknown Is discouraged from being used (aka an incorrect tag) on the osm wiki so it shouldn’t be used; you not knowing if bikes are allowed on a pedestrian path does not need to be tagged, unless there’s a sign saying that bikes aren’t allowed it is implied that you can. For more information see the “ Possible tagging mistakes” section on the following wiki page https://wiki.openstreetmap.org/wiki/Key:bicycle .