How do I check raw signal strength in decibles with an iphone?

I am trying to find the raw cell phone signal strength in decibels.  All of the resources online say to access the field test menu and look for the rsrp value but I think it may have been removed from the menus.  I was also recommended to use a third party app but I haven’t found a legit one that worked.  I called Apple and they said it is an issue with the carrier and not an iphone issue.

Does anyone know how to do this or have possible alternatives?

Thanks!