If you just want a polished offline maps app based on OpenStreetMap data checkout https://organicmaps.app/

Not really. OSMand has been around for ages if all you want is navigation with open street maps.

But that's really not what we want from a maps app, issit?

We want intelligent location data like searching for "groceries" and we want to know wherever the location is currently open etc.

While I hope that - eventually - open street map can fill that need, it can't today.

FTR, location data is shared with Google and Apple regardless whether you use their mapping app or not: already the presence of their software on your device causes that software to send data about the device location to them, on a regular basis. This is used for features like traffic info or how busy with visitors a shop or restaurant is at a given time of day: you usually don't have your maps app open when dining or when grocery shopping.

Furthermore, even if you somehow stopped this sending, both operate multiple network services to help devices establish their location: one bases on devices sending a list of the wifi hotspots they see plus a list of network towers they are connected to, etc. The second service is aGPS, which is a network service that helps devices to locate themselves on the basis of GPS input in a cold start situation.

On Android phones, even if you kick gapps off your phone, it will likely still use aGPS.

I still think it's good to use OSM based apps though, because that brings all the improvements/error corrections from users into OSM instead of some proprietary silo.

I use OsmAnd~ on mobile. Works perfectly. Obviously doesn't do traffic.