Use AirPort Utility as a Wi-Fi scanner with a hidden Setting in the Apple App that usually helps managing your wireless network. We explain how to scan for Wi-Fi with AirPort.
2.4GHz vs. 5GHz
Using Airport Utility to Scan WiFi Networks on iOS
How to Check Your Wi-Fi GHz on iPhone [The Easy Way] - Alvaro Trigo's Blog
Using AirPort Utility to collect RSSI - Wi-Fi Vitae
Wi-Fi Scanner For iPhone With The AirPort Utility App
The Best WiFi Channel Scanner for iOS (iPhone, iPad)
How to check your WiFi frequency before pairing devices in eWeLink app – eWeLink Help Center
The Best WiFi Channel Scanner for iOS (iPhone, iPad)
WiFi Analyzer - XMission Wiki