I've had persistent issues with maintaining a cellular signal since the day I received my iPhone 12 Pro Max. What you're stating does not track with reports by dozens of users in the Macrumors and Apple Support forum thread.
The issue is independent to location, settings, etc ... I've ruled out location by travelling within a 200 mile radius since launch, the dropped cellular issue happens everywhere I go within the T-Mobile coverage area. My previous iPhone 11 Pro had zero T-Mobile network issues, and my family's other iPhone XR's are still connecting and staying connected to T-Mobile with zero issues. Even disabling 5G doesn't help.
Settings can also be ruled out ... the issue still happens on a iPhone 12 Pro Max when setting it up as a new iPhone, after resetting network settings, and even after a DFU restore.
But the biggest evidence that you're take is wrong is that for most users there's a 100% consistent reproducible test case. Simply go to Settings->Cellular, wait about 10 seconds, and your cellular connection will drop and reconnect. I was able to show the issue happen on demand to Apple Support while screen sharing dozens of times over the past few calls with support.
I don't know what other external factors you're referring to other that location and settings, but from where I stand ... the issue looks to be related to either faulty hardware on some but not all iPhone 12 Pros, a bug in iOS, an issue requiring a carrier and/or modem firmware update, or a combination of any of the previously listed factors. Exactly how is that not newsworthy?