I'd suggest Komoot (Komoot.com).
Yep I realise it's another phone app, but it can work on just GPS - doesn't need a phone signal.
It downloads the map to your phone and then it works off just GPS, also does voice navigation with the screen turned off.

You can create the route on their web site (using Open Street Map or Open Cycle Map if you want).

Edit: I'm using it on an old Moto G6