Nearly all trails are unpopular if you start hiking at 6:00 AM (the benefit of being a morning person).😴

I find that the best way to find unpopular trails is, identify trails with a famous popular destination (an overlook, waterfall, etc..) and go there. Then take the other fork away from the famous thing.  This is especially effective in places that locals avoid due to overcrowding since literally everyone is there specifically to see the famous thing.