Well, you can contribute to CoMaps to map your local area — it can actually be quite fun to just walk around and add businesses and the like. Kind of like some of the games that have you walk around and catch creatures in balls, except you map your local community, find new places and spots, and basically contribute meaningful stuff :)

Not sure about Japan specifically, but I use Here We Go. i have also found that Open Street Maps based maps don't have enough info in my area.

Here We Go is sort of a legacy project, currently owned by several European car manufacturers, servers in the Netherlands, a good country for data privacy laws. Basically it costs money to operate a maps app, but it's a rounding error for the type of money they make. Solid privacy policy. Closest in functionality to Google, using TrioAdvisor for discovery/reviews/pictures/business info. Solid at real time traffic. Built in buttons to run in offline mode and delete any data. You can save favorite locations without an account.

It's not perfect though. Closed source. Can't search along route in Android Auto mode, and when you do in normal mode it does not tell you how much time will be added to the trip. Voice assistant doesn't work in Android auto (its no longer installed on my phone though). 2 trackers: Google Crashlytics & Facebook login. You can turn off telemetry in the app though, and not sign into Facebook obviously. You have to download it from Play Store specifically for Android Auto, not even Aurora Store, not even if you enable unknown sources for Android Auto.

I've been looking too but I can't find any specific to Japan. I think you and I are gonna have to add every single spot in Japan.