Unlocked s21 Ultra showing as "Unknown Device" and not supporting 5G or Extended Range LTE on My Mobile account

GriffithMagenta wrote:

I just bought an unlocked S21 Ultra directly from Samsung.  It works great, including the tmobile voicemail app and RCS through the Google messages app.  It says I'm connected to 5G on the phone, and I get 150+mbps download from home on speedtest.net

The problem is that the tmobile account website shows this:

The problems with this is:

1. Most important: I have free phone repair insurance through my Uber Visa Signature credit card.  In the past, when I filed a claim, they required a screenshot of the account to show that I have the device I'm filing a claim for on the tmobile account that I pay monthly through my credit card.  I would have issues proving that I have an S21 Ultra on my tmobile account if it says "unknown device:"
2. I’m worried I’m not getting the best speeds or roaming experience if I were to take a road trip in a rural setting.  150mbps+ from home is good enough in the major city that I live in, and I’m sure it’ll be better if I get closer to the tmobile cell phone tower which is 3 blocks away.

How do I get this phone to show as "Samsung S21 Ultra" instead of "unknown device"?  I don't see any option online to specify this.

Not only that, but in areas covered by T-Mobile's partners you will have no service. This happened to my wife and me. Galaxy Note 20 ultra 5g and Galaxy S20 from samsung. We had no service in Clarksburg WV, when we contacted T-Mobile we were told it's because our devices were not purchased from T-Mobile, and as such are not allowed to roam on the US Cellular network where US Cellular provides domestic coverage for them. Just be aware.