My US model (XQBC62) is has having trouble with 5G on T-Mobile. 5G connects only intermittently in NSA mode.
Sony support says:
I'm asking you this because at this moment Verizon is currently the only U.S. carrier that supports 5G on the Xperia PRO model. The 5G network service is not currently available in the Xperia 1 III model and this is why you're getting that issue. In this particular case we recommend you to check with your phone carrier if there is a way for them either to provide a different network service or if there is a work around on their system for you to use your Xperia phone with their service
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The Xperia 1 III phone does support 5G however at this moment the only phone carrier that provides 5G service on the Xperia phones in the USA is Verizon and at this moment they only support it on the Xperia Pro model. The phone carriers still working on providing the 5G service on all phone models they support and that depends on their coverage. I would like to give you a different solution however the phone service is covered by the phone's carrier and the best option you have is to contact T Mobile directly so they can further assist you with this issue
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I would like to give you a different answer Kevin but at this moment the phone carriers don't support 5G service on the Xperia 1 III model and this function will be available through future updates by the phone carriers.
Sony support says:
I'm asking you this because at this moment Verizon is currently the only U.S. carrier that supports 5G on the Xperia PRO model. The 5G network service is not currently available in the Xperia 1 III model and this is why you're getting that issue. In this particular case we recommend you to check with your phone carrier if there is a way for them either to provide a different network service or if there is a work around on their system for you to use your Xperia phone with their service
...
The Xperia 1 III phone does support 5G however at this moment the only phone carrier that provides 5G service on the Xperia phones in the USA is Verizon and at this moment they only support it on the Xperia Pro model. The phone carriers still working on providing the 5G service on all phone models they support and that depends on their coverage. I would like to give you a different solution however the phone service is covered by the phone's carrier and the best option you have is to contact T Mobile directly so they can further assist you with this issue
...
I would like to give you a different answer Kevin but at this moment the phone carriers don't support 5G service on the Xperia 1 III model and this function will be available through future updates by the phone carriers.