I love Organic Maps. Works on Android and IOS. Fully offline (maps predownload at first run) and all route calculation is locally computed so it's especially good for hiking or where signal is poor.

Only thing I miss is live traffic updates but for me that's an acceptable tradeoff for the ultimate offline privacy as far as a digital map can do it.

The voice it uses is whatever's built into the phone's accessibility features so on some devices it sounds a bit janky, but on Android at least you can install different ones if that bothers you.