I use OsmAnd offline map app. It has most trails, but not all.

>>2848057
Osmand is based. Make sure you download from FDroid to get the free premium version.

it's kinda a racket cuz they are the only game in town (yes I know there's other apps but they are much harder to use)
but, in my experience, the actual app works ok
other than deeply annoying shit like them removing the ability for you to load exact locations of other people's previously taken photos in the app and to load the photos itself so you could see where the best views were and line yourself up with that location in confusing places
they really need a better system of being able to click on a map and clearly see exactly where the best views are and what they look like, now you basically have to plan that in advance and pre-screen trails and photos to see where you want to go and if it's worth it
AND
more damagingly, they removed the "community content" feature so now you can search by individual users but there's no way to do a map-view search anymore where you can see all the user-submitted trail recordings in a given area (plus photos) so you could find lesser hidden gem trails beyond the alltrails curated ones