iPhone 12 has fully signal bars but no data (iOS14.5.1)

Does anyone have the same issue with me, it happened last week Wednesday when I updated the system to iOS14.5. My iPhone 12 pro can make phone calls, can send messages to other guys, but NO data. My data plan is unlimited. The signal bar is 5G, but no network.

I tried everything, reset all settings, erase all data and contents, that does not work. I went to the T-mobile store, they replaced a new 5G SIM card for me, but it did not work. I went to the Apple store, they thought it is a hardware or antenna issue, they changed it but still not work. After that, they replaced a new phone for me, but the issue still not resolved. They told me it has to be the carrier problem. I went to T-mobile again today, I do not know what they did on my phone, but finally, it was working, it can open websites on cellular data. But again, 2 hours ago when I was outside, the cellular data just suddenly disappeared. I tried to restart, reset all settings, it still does not work.