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I use Memory Map for navigation with OS maps in the the UK, but off to Italy and France this month and MM no longer offer topo maps for these countries, sadly.
So looking for another app to use that's reliable and allows offline map usage. Don't need auto-routing or turn-by-turn navigation, just want to load a GPX and follow it. Preferably proper topo maps, e.g. IGN, which I don't mind paying for, but OSM/OCM might have to do.
Not Outdooractive, it's rubbish, runs slowly, and eats battery.
Have a look at Backcountry naviagator  worked in France and easy to overlay gpx files . There is a lite and pro version but lite seemed to work fine .
We have Cartes IGN as an app. Didn't have to pay for it
Use it as a last resort if I can't find what we are after elsewhere
Locus Maps and select the Open TopoMap General.
It's free and you can select and download the specific areas you want.
It has navigation, too.