iPhone 12 pro Max Issues?

in which country you r using ur iPhone 12 Pro Max?

I'm on day three with my 12 Pro Max and it's perhaps the best, most stable iPhone I've owned and I've had LOTS of them.

For cellular, go to Settings > Cellular > Cellular Data Options > Voice and Data -- What is it set to? If you have 5G On, you should choose 5G Auto or perhaps just LTE if your cellular provider isn't yet broadcasting in 5G or perhaps you aren't paying for a 5G capable plan.

You said you've restarted your phone. Have your Force Restarted, by following these directions:

1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Press and hold the side button.
4. When the Apple logo appears, release the button.

Another thing which could be happening is you brought something over from your previous iPhone which is causing issues with your new phone. If the two suggestions I provided above don't help, you should give consideration to restoring your new phone back to factory and bringing things over slowly to see what if anything may be causing your issues.

FYI: These are user-only forums. Apple's presence here is very limited. If you want to provide direct feedback to Apple then please leave feedback here ➔ Product Feedback - Apple

Axel F.