Organic maps is the best alternative I could find. It’s on Accressent which you can get from the GrapheneOS App store. All the maps you want are downloaded to the device, no need for network access afterwards / continuously. Pathfinding is fast compared to e.g. Osmand. It’s pretty barebones though.

Kinda sad that Adobe bought them and will probably kill the product in an EEE scheme or merge it into Adobe XD.