Apple has altered the way it displays mobile data connectivity on the iPhone 12, which some users might find misleading.

An early review of the iPhone 12 found the status bar displays the best available mobile data connection, rather than the speed currently in use. So, even though you may see ‘5G’ to the right of the display notch, you may still be accessing 4G LTE speeds.
…
Continue here:
https://www.trustedreviews.com/news/iphone-12-5g-status-bar-4105169