I use OnX Off-road and it’s awesome! I’m in the Sierra Nevada near Yosemite and there is very patchy cell signal off-road in the forest but I can download hi-res offline maps in the app and the phone GPS keeps me spot on to my track.
I’ve looked at others but nothing has the database of Offroad trail that I’ve found in OnX
Unfortunately:
So, like others, I use an old Android and Maps.me, combined with the Open Street Maps (OSM) maps it allows me to plan a ride from my couch on my PC browser, and then using the same map the Maps.me app on the Hunter Cub.
The OSM maps are fully populated with government survey details, including all trails, walking tracks, and similar.
Coupled with the contours, it makes for a great mapping experience.
Further, the app - with downloaded maps - is entirely self contained and does not need cell coverage to provide either moving map or navi capabilities.
No cost, no ads, and totally reliable (if it can see a bird that is), and since I've been using it, it has never let me down.
For the paranoid too, you can connect to wi-fi, download the app, download your maps, and without a valid SIM and wi-fi turned off you are essentially dark and in total receive GPS signals only stealth mode.
My only issue is the old Android battery lasts just a few hours, and I need to add a USB port to my Cub, but that's another issue...