This is an app that allows you to check whether 5G is Sub-6, millimeter wave, diverted 5G, or anchor band.
Also, if you are connected to 5G, you can check whether you are using standalone (5G SA) or non-standalone (5G NSA).

If it switches to 4G after communicating even though it is 5G, there is a high possibility that it is an anchor band.

There is a widget function, so you can check it even from the home screen.
There is also a function that allows you to check the notification icon even in the background.

This app is open source. You can check the source code from here.
https://github.com/takusan23/NewRadioSupporter