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

Apparently in the situations mentioned, it's about Samsung phones -- unlocked -- not being compatible with SOMETHING within T-Mobile. Maybe the SIM cards they provide for the unlocked phones aren't set up correctly. Maybe it even has something to do with an almost passive aggressive way of 'discouraging' customers to buy products directly from Samsung.

Whatever it is, it has wrecked the fun and excitement of my new phone.

Interestingly, before I realized what a mess this was going to be, I took advantage of the Samsung watch offer on 2/24. The data lines were added last night, and the phones are being delivered tomorrow, 4/7. I just hope it goes well.