I’ve recently discovered Organic Maps that allows offline viewing of open street maps. I’ve been using it since maps.me has completely gone down the drain with premium subscriptions and paid download limits (for the same open street maps data lol).
Check out StreetComplete. It shows you missing osm data close to you so you can add that information directly. Very good way to get highly detailed information into OSM, like accessibility for stairs (handrail, ramps, etc.) or opening hours for shops (including updating older data)