Filesystem:/Applications/FTMInternal-4.app
From The Apple Wiki
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FTMInternal-4 is a hidden system app on iOS devices that provides detailed information about your cellular connection, including signal strength, cell tower data, and network statistics. It's commonly referred to as Apple's Field Test Mode. This tool is primarily intended for network engineers and developers to analyze radio conditions.
You can open FTMInternal-4 by opening the Phone app and dial
*3001#12345#*