Go to Settings > WLAN and touch the name of the Wi-Fi network you are currently connected to view basic information about the network . From here you can view if the Wi-Fi network is a 5 GHz network or a 2.4 GHz network.
Read moreHow do I find out if my WiFi Router is 2.4GHz or 5GHz on a Mac?
To check whether your Wi-Fi is using the 5GHz or 2.4GHz channel on a Mac you simply need to click on the Wi-Fi icon in the top nav bar while holding down the Option/Alt key . This will give you a bunch of information on your Wi-Fi, and in the middle it will show which channel your Wi-Fi is using right now.
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