I am not sure of your Location/Country but once you find your gravel/dirt roads very often the map will not show the full path of the Gravel/Dirt road.
Taking Wolvens Lane (In the Surrey Hills) as an example the Here map only shows part of Wolvens Lane with a big chunk missing in the Middle.
Snapshot 22-10-2023 17:04.jpeg
Once you are on the route itself you can then just follow the the actual gravel/dirt road in full.