Not sure if you're looking for paved or unpaved backroads, but if it's the latter I recently shipped a feature at my day job (https://ridewithgps.com) that highlights all unpaved backroads, visible up to zoom level 8 (above zoom 8 we start running into tile size/data limitations).
May be useful to you or others in this thread. We lean pretty heavily into the "cycling power user" market segment, the feature set isn't always the most discoverable but it's quite comprehensive if you put in the up-front time to learn the tooling (similar to a lot of other specialty mapping apps out there - caltopo, fatmap (rip) etc)