Network settings on iPhone 12 Pro Max changed from cellular data to mobile data

It means the same thing. In the US, they generally refer to it as cellular data. I've seen in other countries, it is referred to as mobile data. Cellular, Mobile, all means that you are connecting to your phone carrier.

Your carrier decided to change it. My carrier (AT&T) is still calling it Cellular Data.

I'm on AT&T as well, and mine says cellular. Over the years, I've seen carrier in the UK call theirs mobile data.

Do you have a screenshot you can share? Here’s mine,