All I need is good GPS/mapping features that doesn’t connect to my phone what so ever.

As others have pointed out, a throwaway phone would likely work best for this use case.

I use an old Samsung phone with OSMAnd (uses Openstreetmap data), but it can also run whatever other mapping software I could possibly need. For example, we had a local community ride, and they required us to use Ride with GPS, which I never used before. No problem. A bike computer with GPS nav would have made this more difficult.

If you plan to ride for more than 3-5 hours at a time, a phone may not be best, unless you’ve got it connected to a powerbank.