If you do a search of these fora you'll find a lot of info.
On the assumption that you already have a route planned and just want to follow it, I recommend Osmand. It's free (at least within a pretty large area) and works offline. However it does take effort and application to get familiar with it. In my opinion well worth the effort.
Komoot requires the purchase of maps at a one off cost, although they regularly offer discounts on worldwide maps.
RWGPS requires an ongoing subscription to navigate. There are others such as bikemap as well. An issue with the subscription apps is that they can regularly change what features are provided in the packages they offer, including the free ones. One reason to prefer Osmand.
If you need a route planner as well, that is a different question.
