I did contact support and they said/did
"We've made a configuration change on the back end of the account. Please log out of the Go app and then back in to ensure the app UI reports the correct information on the account after the configuration we performed."
The result was they did deactivate the 5ghz radio which I should be able to successfully do myself.
I asked them if I need to contact them every time I need to do this. No answer yet.
This topic has been around for at least 3 years and I am wondering if they will simply resolve the issue. The settings are in the UI but the best I can see that the settings do is HIDE the 5ghz network, not turn it off, which in some cases is good enough but..